What Changed in the Passing Game: Volume II

Yesterday, it was discovered that the pass blocking and drops by pass catchers went from really good to about average.

The hypothesis, then, is that the quarterback was largely responsible for the Bears having one of the worst passing games – and thus worst offenses – in the NFL. So today I want to look at Mitchell Trubisky’s performance more closely to see what it can tell us.

On the surface, Trubisky certainly was awful in 2019. He completed 63.2% of his passes (18th in the NFL), averaged 6.1 yards/attempt (last), and posted a passer rating of 83.0 (28th). This was a big step back from 2019, when he was near average in all of those marks (66.6% completion, 14th; 7.4 yards/attempt, 18th; 95.4 rating, 16th).

Evaluating a quarterback’s play statistically can be tricky, because his stats depend both on his offensive line’s ability to block for him and his RBs/WRs/TEs’ ability to catch his passes, both of which are outside of his control. That’s why I started by looking at the offensive line and drops, both of which were worse in 2019 than 2018 but not nearly bad enough to explain bottom 5 production from the quarterback.

It’s also worth noting that Chase Daniel’s production barely changed between seasons. In 2018, he completed 70% of his passes, averaged 6.8 yards/attempt, threw 3 TD and 2 INT, and posted a 90.6 passer rating. In 2019, he completed 70% of his passes, averaged 6.8 yards/attempt, threw 3 TD and 2 INT, and posted a 91.6 passer rating. To be fair, it’s a small sample size – he played 2 games and threw around 70 passes each year – but still, this is at least anecdotal evidence to support the notion that the offense as a whole didn’t change all that drastically.

Advanced Stats

With that said, let’s look more closely at Trubisky’s performance to see if we can hone in on what changed, besides worse pocket presence and less running impact, which were touched on in previous articles. This is going to focus on passing. We’ll start by looking at a smattering of advanced statistics, which come from a combination of Next Gen Stats and Pro Football Reference.

A few thoughts:

Let’s start with stats that didn’t change: Trubisky threw the ball in about the same time each year, and had the same rate of “bad throws.” This is an admittedly subjective stat from Pro Football Reference, but I included it because it highlights the fact that Trubisky’s accuracy problems aren’t new. They were present in 2018 as well, and I wrote about them last offseason, especially on deep passes. The problem is that new issues cropped up in 2019, which I’ll get to in a second, and previous strengths (running and avoiding sacks) vanished, drastically tilting the good/bad ratio Trubisky displayed in 2018 towards the bad.
I grouped stats by color that are related to the same thing. All of the blue ones, for instance, tell us about how far down the field Trubisky’s passes were targeted. Here we can see that Trubisky both attempted and completed shorter passes in 2019 than 2018. He had the 9th shortest average completion, ahead of only Mason Rudolph, Devlin Hodges, Teddy Bridgewater, Drew Lock, Derek Carr, Joe Flacco, Jacoby Brissett, and Kyler Murray. As that list shows, you can make it work with a short passing style, but it’s generally not the approach you want to take. For what it’s worth, Trubisky played with a similar checkdown, play it safe mentality in the final few weeks of 2018, only he did it much less efficiently.
It’s also worth noting that keeping a consistent bad throw rate on shorter passes is actually getting less accurate, though the correlation between average target depth and bad throw rate was not nearly as strong as I suspected it would be.
The orange stats both tell us something about how open the players Trubisky targeted were. Despite attempting shorter passes, Trubisky threw the same rate of aggressive throws (into a player who has tight coverage). For comparison, when he threw similarly short late last year, only 15.6% of his throws were aggressive. Derek Carr and Teddy Bridgewater, the 2 best QBs who had shorter completion distances this year, both had aggressive throw rates below 14%. The expected completion percentage, which factors in both depth of the throw and how open the target is, also dropped despite shorter passes, indicating Trubisky was generally throwing to players who were not as open. If you’re going to be a short passer, you have to find open guys, and Trubisky was not able to do that in 2019.
Yards after reception (YAC) also went down in 2019. In general, Chicago’s pass catchers have struggled in this area, with 6 of the 7 who qualified for next gen stats over the last 2 years coming in below their expected value. I think this is a combination of routes run (they throw a lot of curls, which have very little YAC) and an inaccurate QB forcing them to break stride, but I can’t say for sure.

By Target

So one of the reasons Trubisky struggled in 2019 is that he threw too short of passes and wasn’t able to find open targets on those short passes. Now I want to look at how that changed a bit by different positions who were targeted. To do so, I’m using advanced receiving stats from Pro Football Reference. I’ll note these aren’t Trubisky-specific, because they don’t let you sort by that as far as I could find, so Daniel’s throws in each season are included.

A few thoughts:

Here we see the shorter passes came exclusively at TE and RB. Most of the passing targets to running backs went to Tarik Cohen, who decidedly had a down year in 2019, but his average catch depth went from 2.9 yards to 0.3 yards. He basically caught the ball, on average, at the line of scrimmage, which is ridiculous for somebody with 100 targets.
We do see the TE issues crop up again in where passes were targeted to. Tight ends lost a 6% share of targets from 2018 – about 30 over the course of the year – and they were switched to WRs.
Catch percentages really didn’t change much once you account for drops (as I said before), but yards per target drops across the board even after removing drops from the equation (by adding on expected yards if all drops turned into average completion to that position).
Pretty much across the board here we see the stats drop from 2018, but the dropoff is larger at TE and RB than for WR. Worse efficiency for WRs is pretty remarkable considering most fans would argue Allen Robinson and Anthony Miller were both better in 2019 than 2018, and they got a larger share of the targets in 2019 as well. The dropoff at WR despite this tells me that the QB play was worse in 2019 than 2018. The substantially larger dropoff at RB and TE tells me those positions were also worse in 2019 than 2018.

Finally, this last chart shows general stats for Trubisky-only targets from 2018 to 2019. I couldn’t get advanced stats for them, but we can at least see if the same pattern holds up. I grouped the targets slightly differently to try and do as many direct comparisons as possible.

Here we see the same pattern hold true. Yards per target actually got worse for every person/group but Anthony Miller. It took the largest nosedive for Tarik Cohen and the tight ends, which makes sense for reasons discussed above. I think the dip in production from the “other group” also highlights the issues with quarterback play. In 2018, that was mainly Josh Bellamy, Jordan Howard, Kevin White, and Taquan Mizzell. In 2019, it was largely David Montgomery, Javon Wims, and Cordarrelle Patterson. Most would agree the 2nd group should be better and more productive, but they weren’t.

Blame the quarterback. It’s a fair argument that there were factors outside of his control (TE injuries, pass blocking, drops) that hurt Trubisky’s production, but none of that comes close to accounting for the seismic statistical dropoff he saw from 2018-19.