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What Changed in the Passing Game: Volume I

| January 22nd, 2020

It stands to reason that if the offense was mainly responsible for the Bears’ 2019 regression, and the running game didn’t change all that much, most of the regression came from the passing game. And a quick look at the stats backs that up. In 2018, the Bears were 9th in completion percentage, 18th in yards/attempt, 14th in passer rating, and 10th in sack percentage. In 2019, those ranks fell to 14th, 32nd, 24th, and 23rd.

So what went wrong in the passing game? Generally, there are 3 components to examine: the pass protection, the pass catchers, and the quarterback. Let’s look at each one by one.


Pass Protection

Evaluating pass protection statistically is difficult, but thankfully advanced statistics to help with this are getting better. A number of them are shown below, with their ranks out of 32 NFL teams in parentheses. Average time to throw is from Next Gen Stats, Average time to pressure and pressure rate is from Pro Football Reference, and Pass Block Win Rate – a measure of how often a QB has a clean pocket for at least 2.5 seconds, is from ESPN Metrics (source for 2018 and 2019).

 

As I tried to make sense of these numbers, it seemed to me that the change in NFL ranks was often greater than the change in the actual value. Sure enough, it seems that pass blocking was slightly better across the league in 2019 than 2018. The median average time to pressure increased from 2.4 to 2.5 seconds, the median pressure rate dropped from 24.1% to 22.6%, and the median pass block win rate increased from 50% to 59%.

Looking just at the Bears’ numbers, they generally got a little worse in pass protection, but their drop in the rankings looks worse than it is because the rest of the NFL got better. The average time to throw didn’t change all that much and the pressure got there a little faster, but the Bears still ranked right around average both in pressure rate and pass block win rate.

If the pass protection didn’t get much worse, how do we account for the massive uptick in sacks? The Bears went from giving up 33 sacks in 2018 (6.1% of dropbacks) to 45 in 2018 (7.2% of dropbacks).

Well, sacks aren’t only due to the pass blocking, they’re a result of the quarterback as well. Lester Wiltfong of Windy City Gridiron breaks down film on every sack and assigns blame to the person or people he deems responsible (he also splits blame if multiple people mess up).

In 2018, he had the quarterbacks responsible for 8 sacks (6 by Trubisky), but that number jumped to 17.5 (15 by Trubisky) in 2019. Blame on the offensive line, by comparison went from 12 sacks in 2018 to 19.5 in 2019. This supports the notion the the pass protection was worse in 2019 than 2018, but still not all that bad, and a large part of the increased sacks allowed is due to quarterback play. Mitchell Trubisky was excellent at using his legs to avoid sacks in 2018, but that stopped in 2019, and the offense suffered because of it.


Pass Catchers

We can also look at the guys catching passes to see how their performance changed from 2018 to 2019. Like with the offensive line, there’s no denying there was some regression here. Pro Football Reference credits Chicago’s targets with dropping 5.5% of Trubisky’s passes in 2019, the 12th highest mark in the NFL. In 2018, that number was 2.6%, the 2nd lowest mark. This increase of 2.9% coincides strongly with Trubisky’s dip in completion percentage of 3.4%. It’s also accounts for why Trubisky completed 1.7% more passes than expected in 2018 (according to next gen stats) and 1% fewer than expected in 2019, a net difference of 2.7%.

It’s worth noting that the median quarterback has had around 5% of their passes dropped over the last 2 years, so 5.5% really isn’t all that bad (thus 12th highest rate, when the median is 16th of 32 qualifying quarterbacks). Really, 2018 was an unsustainably low rate of drops, and 2019 saw that regress towards (and a little past) the mean.

And drops don’t come close to fully explaining the yards/attempt decrease we saw. Trubisky averaged 7.4 yards/attempt in 2018 and 6.1 yards/attempt in 2019, a dropoff of 1.3 yards per attempt (or 670 yards over the whole 2019 season). His average completion went for 9.6 yards, so if we assume the drop rate was consistent with 2018 (when it was the 2nd best in the NFL), that would add in an extra 13 catches, or 129 yards, to Trubisky’s season total. That would bring him up to 6.4 yards/attempt, still a full yard lower than 2018.

Like with pass blocking, we see that the pass catchers were not as sure-handed in 2019 as 2018, and their regression there pretty much completely accounts for Trubisky’s drop in completion percentage in 2019. The increased drops, however, only account for about 1/4 of Trubisky’s dropoff in pass efficiency.


Lessons Learned

Pass blocking and avoiding drops were two areas where the offense was among the best in the NFL in 2018 that could not sustain their success. However, they were still not nearly bad enough to account for one of the worst passing offenses in the NFL.

Thus it stands to reason that quarterback play is the primary culprit for regression in the passing game (and thus the offense as a whole) in 2019. We’ll look into that hypothesis next time to see whether it holds up.

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