How Should We Evaluate a Defense?

[HardRightEdge]

From Demovsky, 10/12/18:

"The Packers rank fourth on defense in total yards allowed, but even coordinator Mike Pettine thinks that's deceiving. However, he said, "we feel good about where we're headed." He thinks there should be something akin to passer rating for QBs to better judge a total defense. For example, they didn't give up a lot of yards in the loss at Detroit because the offensive turnovers led to short fields."

I agree that gross yards number is decieving. Points surrendered can be deceiving as well, which I'll get to in a bit. However, a defensive number does exist that equates to QB passer rating: passer rating against, which was 101.9 for the Lions.

That QB rating against is more relective of defensive performance than the gross yard total, but that's one game and is not the entire picture over 5 games. Passer rating agaisnt does not even qualify as an advanced analytic, nor any of the other data below, suggesting Pettine is an old school, eye test guy who may have a nascent interest in statistical analysis. Whether he should or shouldn't advance that interest is debateable, but it should not stop us from taking a statistical view of things.

The passer rating against taken together with a few others, can be revealing. The following data is from espn.com (except where noted) through week 5 (except gross numbers include Eagles/Giants through week 6):

Passer Rating Against: 89.3 - 12th.
Sacks: 16 - 4th. (Note: Sacks are not imbedded in the passer rating.)
Yards Per Carry Average: 4.2 - 20th.
Recovered Fumbles: 2 - tie 17th. (Note: INTs are imbedded in the Passer Rating Against)
3rd. Down Coversions: 38.0% - 14th.
4th. Down Coversions: 0% - tie first (0 - 2)
Red Zone TD% Against: 62.5% - 21st. (from teamrankings.com)
Defensive Penalty Yards: 262- 12th.
Defensive Penalty First Downs: 14 - tie 27th.

Compared to 2017:

Passer Rating Against: 102.0 - 31st.
Sacks: 37 - tie 17th. (Note: Sacks are not imbedded in the Passer Rating Against)
Yards Per Carry Against: 3.9 - tie 8th.
Recoverd Fumbles: 11 - tie 7th. (Note: INTs are imbedded in the Passer Rating Against)
3rd. Down Coversions: 42.8% - 28th.
4th. Down Coversions: 80% - 30th. (8 - 10)
Red Zone TD % Against: 65.2% - 30th. (from teamrankings.com)
Defensive Penalty Yards: 789 - 25th.
Defensive Penalty First Downs: 25 - 8th.

Observations:

• I'm not a big fan of gross points against which I've omitted above. That number takes a lot of scrubbing to get to meaningful rankings which I'm not willing to do. First, TDs surrendered by the offense (pick 6, fumble TD returns) have to be excluded along with any surrendered by the special teams. You'd also want to account for events such as a return team fumble on the 1 yard line ). Then there's other affects of the offense on and special teams on ranking scoring against a defense. How do the relative offenses perform? Which offenses have turned the ball over in their own territory compared to others? Which stay on the field vs. those that get off quickly? Which offenses don't move the ball effectively surrendering poor field position? How about special teams providing advantage or disadvantage in field position? Lots of scrubbing required. Points against is likely meaningful at the top and bottom of the rankings. In the middle 20 or 25 the scrubbing of data could yield a significant shuffling of the rankings.

• One major quibble I have with commonly quoted yards-against numbers is they omit penalty yards surrendered. For example, the Packers 262 penalty yards surrendered is 50% of the yards surrendered on the ground, a non-trivial component. Or consider, for example, that the Packers have surrendered more defensive penalty yards than the Bears have surrendered on the ground (256)! And some of the factors noted above as to how an offense affects the defense apply here as well. If anything, yards per play (including penalty yards) is a better measure. That number would take a lot of work I'm again not willing to do. Conversely, and counter intuitively, a high powered offense that scores early and often, can impact defensive yards surrendered negatively. Teams playing catchup against a defense that rightly assumes a prevent posture to one degree or another are on balance going to run more plays by passing and gaining more yards.

• How meaningful is a 3.9 rushing average against (generally regarded as "good") vs. 4.2 (lower end of mediocre)? Trivial. If a team runs a ball 30 times, the difference in those averages is a scant 9 yards over a full game.

Grading

So, given how offensive and special teams preformance can affect a defense, how can we evaluate a defense independent of offensive and special teams performance?

• Given the emphasis on passing in the NFL which seems to grow year by year, the QB rating against is critical. If we drop QB runs from the run play total (mostly scrambles and kneel downs mixed in with a smattering of option and called runs), I'd guess the passing game is running meaningfully above 60% of snaps, though again that would take a lot of work to get a precise number. Taking Denver as an example, right in the middle of the pack in rushing attempts, you end up with 205 pass plays vs. 120 non-QB runs (Keenum's had only 3 runs), for a 63% vs. 37% split after making the above adjustments. Percentage yards and TDs passing vs. rushing are more stark.

• As a reminder, the passer rating is calculated by a formula that uses 4 basic stats: completion percentage, yards per attempts, TDs as a % of passes, INTs as a percent of passes. It works pretty well. I have one quibble. Strip sack lost fumbles should be included, with a "QB turnovers" stat taking the place of INTs in the formula. No matter how good or bad an offensive line might be, a player is always to be held accountable for ball security. Thats a side quibble that would require a ton of work to suss out.

• Next, how quickly does a defense get off the field with the least amount of damage? "Stops" are an excellent measure: 3rd. down, 4th. down and red zone performance forcing change of possession and forcing FGs instead of surrendering TDs is an efficiency complement to QB passer rating. The affect of sacks and penalties are imbedded in "stops".

• In comparing 5 games in 2018 to 2017's full season, it is best to look at rankings rather than percentages or 2018 gross numbers extrapolated to a full 16 games. Typically, offenses run ahead of defenses in the early season. As the weather starts turning sour and defenses adjust to new offensive wrinkles, offensive production typically ticks down. This year is probably no different with offensive productivity running hot so far. For example, I seriously doubt 11 QBs will end the season with a 100+ passer rating as is the case now.

• In summation, if we take QB rating against together with "stop" performance along with fumble recoveries (INTs already imbedded in the passer rating), you get a fairly representative quick-and-dirty picture of defensive performance independent of the offense and special teams.

• Let's not grade on a curve. I woud divide league rankings into approximate quintiles with the following grades: 1st. -6th. = A; 7-13 = B; 14-19 = C,; 20-26 = D,; 27-32 = F, based on the metrics in the above paragraph.

Pettine (5 games)

The grade is based on the 3 key metrics in the above paragraph.

• I give Pettine an overall C+.

• That grade does not reflect improvement over a dismal 2017, which is considerable, so overall performace should be considered a solid B or maybe better.

• The passer rating against and 3rd. and 4th. down stops taken together earn a net B- grade; the red zone TD% drags down the overall grade. Two fumble recoveries is middle of the league pack.

• Obvious areas for improvement are are red zone defense and penalty reduction as penalties bleed into stop stats.

Capers (2017)

• I give this dismal performance an F+.

• The QB rating against reflects the fact that this defense turned the league's QBs, in the aggretate, into Hall of Famers. If one was impressed with Kizer's performace against the Packers (sans the picks) as evidence of potential, consider the opposition.

• The performance in stopping opponents on 3rd. down, 4th. down, and in preventing TDs in the red zone was nothing short of abysmal.

• The fumble recoveries were a very good B level number, but not enough to earn more than a + tacked on to the F in light of the terrible 28st. -31st. rankings in the other critical categories.

• "Fire Capers"? Indeed, and long overdue if you ask me. Petine is on the road to recovery.

 

[Mondio]

#4 defenses don’t give up 4 tds in 4 red zone trips. They yield fgs when put in bad spots, not 4/4 tds

 

[HardRightEdge]

#4 defenses don’t give up 4 tds in 4 red zone trips. They yield fgs when put in bad spots, not 4/4 tds

Clearly. Nobody stops the opponent all the time in the red zone, but half the time gets you an 11th. rank so far this year or for all of last season. That would be pretty good.

I would put just a little color on that 4/4 by saying 1st. and goal on the 1 after the punt "fumble" is an awfully tough stop for anybody. They also held Detroit to 1 yard and a FG on a 1st. and 10 at the 22, which is pretty close for government work.

All-in-all, the Detroit red zone performance was pretty bad. For the season, the Packers 62.5% TD % against in the red zone, 21st. in the league, is not a good number.

 

[gbgary]

the eye test says they're much better. just inconsistent. better 2nd halfs than 1st's. one complete game so far (buf). can't put the det game on them.

 

[rmontro]

Well, we did have that shutout. The defense looks improved, but it's still a work in progress. Hopefully headed in the right direction.

 

[McKnowledge]

Honestly, a good defense should be evaluated by whether you "set and forget" in fantasy barring the bye week.

 

[Mondio]

I gave them a pass on the 1. The defense is better, and I never expected massive quick turnaround. This defense will a work in progress all year and still won’t be at their best. They are improved. I’m encouraged. Can’t wait to get Alexander back in the field and see what Breeland has. If King can shake all the injury crap, I think we’ll be able to cover long enough for the rush to get there.

 

[HardRightEdge]

Honestly, a good defense should be evaluated by whether you "set and forget" in fantasy barring the bye week.

Fantasy football is meta-football largely detached from what goes into winning and losing actual football games. On the few occasions I've wandered into that meta-domain, I find things ranging from the unfathomable to the inconceivable.

So, just now, I googled how "how are fantasy football defenses scored" and the first link with a list of scoring parameters that came up was this:

http://www.nfl.com/fantasyfootball/help/nfl-scoringsettings

In this case it's Defense + Special Teams given there are points awarded under "Defense" for KO and punt return TDs.

6 points are awarded for a return TD and what appears to be 8 points for a pick 6 or fumble return TD. Compare to the 6 point difference between allowing 1 point on the scoreboard (which is not even possible so lets call it 2 points) and allowing 27 points on the scoreboard. Does that make any sense? I don't think so, especially if they subtract the opponent's defensive or ST TDs from the scoreboard. They don't say so. I presume not. Either way, there's not much sense in that.

Or consider a defense pitching a shutout with, for example, 6 sacks, 3 turnovers and a defensive TD, a truly dominant performance, yielding 28 fantasy points. That's the same as a an offense's dismal 200 yard passing day (a 200 yard QB + 200 yards from the mix-and-match receivers) with no TDs among them. Silly.

I could go on in trying to explaing why it is constructed this way in appealing to the aspects of the game fans find most interesting, but I won't.

I would amend your assertion to say "a good fantasy defense should be evaluated on whether you set and forget..." based on the defensive scoring parameters of that particular league. It's a closed loop within the meta-domain of fantasy, detached from the realities of winning and losing.

Of course this is just one fantasy scoring system. Perhaps there's one that makes more sense. Of the few I've looked at they share similar characteristics.

 

[GB2016]

This D would take a step forward without HHCD. He is responsible for most of the redzone TD's being out of position and terrible ball skills.

 

[rodell330]

This D would take a step forward without HHCD. He is responsible for most of the redzone TD's being out of position and terrible ball skills.

Exactly why I created a thread proposing to trade him. He is only concerned with getting ints and is usually out of position or late. No way should GB break the bank to retain him this off season. Someone said he was the 7th ranked safety in the NFL. Well who the heck cares if he’s giving up deep completions and touchdowns in the middle of the field.

 

[rodell330]

#4 defenses don’t give up 4 tds in 4 red zone trips. They yield fgs when put in bad spots, not 4/4 tds

Bingo. Easy touchdowns at that

 

[rmontro]

This D would take a step forward without HHCD. He is responsible for most of the redzone TD's being out of position and terrible ball skills.

Is that what "set and forget" means? Our secondary gets set for the play, and then forgets who or what they're supposed to cover?

 

[thequick12]

Might as well make the trade for Patrick Peterson not sure what Arizona is asking for but I'd give up one of the two first round picks. I guess at this point that'd be the saints pick. He's 28 years old and under contract for 11 and 12 million going forward to 2019 and 2020. So you get 2.5 seasons of all pro corner play at a reasonable price for a 1st round pick in the late 20's. I'd say do it as fast as we can

 

[HardRightEdge]

[HHCD] is responsible for most of the redzone TD's being out of position and terrible ball skills.

I believe that to be incorrect. Over the last two years I've seen a lot of blown coverages by the other guys where Clinton-Dix just happened to be the guy closest to the ball.

 

[Deleted member 6794]

Football Outsiders' DVOA rankings might present the best available metric to evaluate a defense. The Packers unit was ranked 17th according to them entering week 6.

Their grading system is explained here:

https://www.footballoutsiders.com/info/methods

This D would take a step forward without HHCD. He is responsible for most of the redzone TD's being out of position and terrible ball skills.

Clinton-Dix is an above average safety who has stabilized the play at the position ever since being drafted. The Packers better have an adequate replacement for him on the roster if they decide to move on this offseason as it seems fans have already forgotten about the terrible play at safety for years before his arrival.

Might as well make the trade for Patrick Peterson not sure what Arizona is asking for but I'd give up one of the two first round picks. I guess at this point that'd be the saints pick. He's 28 years old and under contract for 11 and 12 million going forward to 2019 and 2020. So you get 2.5 seasons of all pro corner play at a reasonable price for a 1st round pick in the late 20's. I'd say do it as fast as we can

The Packers should definitely not trade one of their first rounders next season for Peterson. They have enough young talent at the position to pass on him.

 

[HardRightEdge]

Football Outsiders' DVOA rankings might present the best available metric to evaluate a defense. The Packers unit was ranked 17th according to them entering week 6.

Their grading system is explained here:

https://www.footballoutsiders.com/info/methods

The general approach makes a lot of sense, but it's another black box. We cannot see inside as to how the varying outcomes of varying plays are weighted in the rankings. We've seen oddities in PFF grading, such as the aggregate grade being higher than any of the more granular grades, without explanation. Whether PFF or Football Outsiders, the scoring has to be taken on faith.

We encounter black boxes all the time, particularly in the world of finance. An algorithmic ETF or hedge fund, for example, claims a certain objective. We may not see inside how the algorithms operate, but we can evaluate its performace over time against external benchmarks. For example, does an ETF which claims low volatility outformance against the S&P 500 in a down market offsetting underperformance on the upside actually perform against that externally measurable objective?

The thing about PFF or Football Outsiders black boxes is there is no external objectively determined reference against which to judge the effectiveness of their algorithms. We're left to compare the grading of one black box to that of another, a closed loop. We know we can't judge the grading of a defense, for example, on yards or points with all of the extenuating circumstances, not the least of which is performance of the offense. We're left to judge the performance of the algorithms by the eye test.

I'm also skeptical of "level of competition" adjustments in grading algorithms such as Football Outsiders. There's an element of infinite regress or circularity in those computations. For example defense A has a "bad" performance against Offense B's "good" performance in week 1. Then Defense A has a "good" game against Offense C in week 2 whereby Offence C is downgraded for having played a previously "bad" defense. But maybe Defense A was actually "good" in week 1 but Offense A was "really, really good" against them. Again, there's no external reference by which to judge and it has an element of chasing one's tail.

Further, a thought occurs after watching KC last night. They get a 28th. ranked defense from Football Outsiders after week 5. Whoever they play next week or next month, and whatever that offense might do, we presume that offense's results will be downgraded by having played against a "bad" defense. However, Houston has been hobbled with a hamstring, with limited snaps in week 5 and none in week 6. Eric Berry has not played since week 1 last season with an Achilles injury. What happens if, in a few weeks, these guys step on the field together and return to something resembling their previous All Pro form? As a predictive tool, no algorithm is going to account prospectively for the sudden improvement in that defense under those conditions. And it would skew the grading of the opposing offense that week based on the "bad" KC defense coming into that game.

The approach I took in the OP, admittedly rudimentary, has the benefit of transparancy. The 3 elements capture most of what constitutes a good defense, without getting into the regress involved in gauging level of competition, or the pitfalls of ranking on points or yards:

• passer rating against rank
• "stop" rankings (3rd. down, 4th. down, red zone TDs)
• fumbles recovered

What it noteably lacks is a measure of whether a defense has a propensity to surrender long runs or contain them. Those runs are uncommon enough to not have a large affect. If there was an easy way to rank that I'd add it to the list. Rushing defense performance, where it most often and most critically comes into play in the aggregate is accounted for in the stop rankings. The ability to cause and recover fumbles might have a run defense contribution imbedded in it.

I didn't create any algothim to weight these factors. My C+ grade for the Pettine defense to date, at the upper end of the 14th. - 19th. ranking "C" range, was an eye test balancing of the three factors with a little Kentucky windage. Others might come up with a slightly different overall grade based on those factors.

Interestingly, the Football Ousiders overall Packer defensive rank of 17th. is a virutal tie for 15th. with Pittsburgh and Dallas. All three are shown as 0.0%:

https://www.footballoutsiders.com/stats/teamdef

One presumes the difference between 15th. and 17th. is a matter of taking their calculation out to 2 decimal positions which they do not display. That difference is presumed trivial.

If we regard their ranking as effectively a tie for 15th., that's squarely in alignment with my C+ grade. Again, that's a blunt performance grade. Pettine's performance grade is higher for improvement over last last season's dismal performance by the same measures. Football Outsiders graded the Packers defense 20th. at the conclusion of 2017, which would be a D+ grade in my scheme. I give that defense an F+, to do with as one sees fit.

One thing we should all agree on is this, from Football Outsiders:

"The popularity of fantasy football only exacerbates the problem [of grading and ranking]. Fans have gotten used to judging players based on how much they help fantasy teams win and lose, not how much they help real teams win and lose."

 

[Cheese Headed Monster]

Don't care how many yards get put up on us through the air. A good defense can stop the run and force FG's instead of TD's. If a team has 4 red zone visits against us, if 2 of those 4 are field goals, I'll be happy. For now.

 

[Dantés]

A lot of good points raised here.

Points/drive is a metric that, in a perfect world, would be very telling. By for reasons you raise, it's faulty (short fields, defensive scoring, etc.).

I like Footballoutsider's DVOA as a metric-- not as an end all, be all, but it's more thoughtfully informed than your typical raw stat.

At the moment, FO gives Green Bay a dead neutral Defensive DVOA of 0.0%, which is also dead average in the league overall (Dallas, Pittsburgh, and Green Bay are all at 0.0% and are the 15th, 16th, and 17th teams in their rankings).

It's interesting that your own analysis gave them a "C+" and FO has them right in the middle as well. I think their ranking makes sense anecdotally as we've seen stretches of excellence and stretches of misery from the Packers' stop unit so far.

For years, fans have said that if only the Packers had an average defense, Rodgers could make some serious noise. It would seem that they now have at least that, but the offense is out of sync. Here's hoping that a weak opponent at home on MNF and a week off will help them pull it all together.

Sorry-- I see this was already being discussed.

 

[Deleted member 6794]

For years, fans have said that if only the Packers had an average defense, Rodgers could make some serious noise. It would seem that they now have at least that, but the offense is out of sync. Here's hoping that a weak opponent at home on MNF and a week off will help them pull it all together.

If the Packers offense is be able to perform up to their potential for the rest of the season this year's defense might be good enough for the team to have a legit shot at another title.

 

[HardRightEdge]

Clinton-Dix is an above average safety who has stabilized the play at the position ever since being drafted. The Packers better have an adequate replacement for him on the roster if they decide to move on this offseason as it seems fans have already forgotten about the terrible play at safety for years before his arrival.

I agree with that. I don't think he's ever been a Pro Bowl caliber safety, as he was judged in 2016, but on balance he's been pretty decent. I think the worst thing we can say about him is he's an inconsistent tackler.

People tend to get fixated on a few bad plays, such as the 2 point conversion brain fart in the Seattle playoff defensive meltdown that always comes up in discussions of that game. Or a few poor plays in this last game against Detroit, where recent memory colors the overall perspective. Clinton-Dix's body of work now encompasses 4,374 snaps according to Football Outsiders.

Here's something to consider. Think about all the plays where you do not see what he is doing, playing centerfield much of the time, off the TV screen. What is he doing? How is he anticipating the throw? Do offenses avoid his territory? Regardless of how bad these Packer pass defenses have been in recent years, we don't see very many offenses challenging the deep middle when he's there or their having an undue amount of success when they go there.

For anybody who watched the KC-NE game, consider the 75 yard TD completion to Hill where he crossed in front of the safety's face into space. What was that safety thinking? Did he get fooled by Mahomes looking him off? I don't care. There was no more clear and present danger than Hill. It didn't even need to be a well thrown ball, and it wasn't. Why stand there looking for work when the obvious work is right in front of you? You don't see C-D making those kinds of mistakes.

While playing with poor CB groups in recent years I've noted on several occasions where he's been left betwixt and between by his teammates not doing what any reasonably attentive observer would think they should. He ends up being the guy closest to the ball with the finger pointed at him.

 

[HardRightEdge]

If the Packers offense is be able to perform up to their potential for the rest of the season this year's defense might be good enough for the team to have a legit shot at another title.

A lot of things would have to go right, a lot of things not go wrong, and some things going wrong for the other guys would need to happen for that be a serious consideration beyond "hope".

The Division is tougher, the schedule gets harder after SF, especially with 6 on the road and 4 at home. After SF, 4 of the next 5 are on the road against LAR, NE, Seattle and MIN. Assuming a win against SF, going 3-2 in that subsequent 5 game stretch would be needed to keep pace. Otherwise, it's 5-5-1 or worse heading into the streatch.

Pristine health, 2nd. and 3rd. year jumps ahead of schedule, contenders going in the opposite direction, 6-4-1 after week 12? That scenario would be worth reevaluating conditions and the odds.

Right now, though, I'd say the best path might be in a Division title. All the other guys still have 5 division games to go where they could beat up on each other . If the Packers could sweep their 3 remaining division games under that scenario I'd say the odds are pretty good but not easy.

 

[Pokerbrat2000]

The Division is tougher, the schedule gets harder after SF, especially with 6 on the road and 4 at home. After SF, 4 of the next 5 are on the road against LAR, NE, Seattle and MIN. Assuming a win against SF, going 3-2 in that subsequent 5 game stretch would be needed to keep pace. Otherwise, it's 5-5-1 or worse heading into the streatch.

This touches on one of the most overlooked variables to me when compiling stats and ranking teams/players based on those stats, that variable is "who" did those stats come against? Maybe by Game 12 and on, you can start using "stat rankings" as a somewhat reliable metric to grade and predict how teams will do in the future, if that team has faced a fair representative of balance in the NFL. So far this season, the Packers have not really faced a high powered offense, so I'm going to hold my breath until the Rams game to see just how much they have or haven't improved.

 

[Deleted member 6794]

The Division is tougher, the schedule gets harder after SF, especially with 6 on the road and 4 at home. After SF, 4 of the next 5 are on the road against LAR, NE, Seattle and MIN.

The schedule is getting extreme tough after the bye week as the Dolphins at home don't seem to be a pushover either. The Packers will have to be significantly improved to win three of the next five games.

 

[Dantés]

Well... Pettine gets an F for gameplanning and an A for adjusting... there's you final grade: C.

That has been a theme with him.

49ers 1st half: 24
49ers 2nd half: 0

Lions 1st half: 24
Lions 2nd half: 7

Bills 1st half: 0
Bills 2nd half: 0

Was 1st half: 28
Was 2nd half: 3

Vikings 1st half: 7
Vikings 2nd half: 22

Bears 1st half: 17
Bears 2nd half: 6

The Buffalo game obviously doesn't fit with the pattern as we shut them out (and they're kind of a negative outlier as an NFL offense, so that makes sense). But otherwise, you have four games where the defense gets shredded in the first two frames and then locks it down a lot tighter after halftime-- the Minnesota game being the lone exception. So what's going on? Can Pettine not come up with an effective gameplan? Are teams just taking their foot off the gas? I don't really think it's the latter-- I don't know why the league would consider a lead safe when Aaron Rodgers is across from you.

Bottom line-- Pettine and his personnel absolutely must find a way to limit teams in the first half.

 

[Deleted member 6794]

Well... Pettine gets an F for gameplanning and an A for adjusting... there's you final grade: C.

That has been a theme with him.

49ers 1st half: 24
49ers 2nd half: 0

Lions 1st half: 24
Lions 2nd half: 7

Bills 1st half: 0
Bills 2nd half: 0

Was 1st half: 28
Was 2nd half: 3

Vikings 1st half: 7
Vikings 2nd half: 22

Bears 1st half: 17
Bears 2nd half: 6

The Buffalo game obviously doesn't fit with the pattern as we shut them out (and they're kind of a negative outlier as an NFL offense, so that makes sense). But otherwise, you have four games where the defense gets shredded in the first two frames and then locks it down a lot tighter after halftime-- the Minnesota game being the lone exception. So what's going on? Can Pettine not come up with an effective gameplan? Are teams just taking their foot off the gas? I don't really think it's the latter-- I don't know why the league would consider a lead safe when Aaron Rodgers is across from you.

Bottom line-- Pettine and his personnel absolutely must find a way to limit teams in the first half.

That's an interesting observation. I don't know about the reason for it but the Packers defense definitely has to play better in the first half in which they rank 29th in points allowed. Only the Ravens have given up less points than Green Bay in the second half.