Johnathan Wood | January 16th, 2018

Former Bears coach Lovie Smith always talked about breaking the NFL season down into quarters, which splits a 16-game season into 4-game sample sizes. I’ve always thought that was a good way to look at it, as grouping four games together helps smooth some of the statistical noise of individual good or bad games.

With that in mind, I want to track Mitchell Trubisky’s rookie season through the quarters lens. Trubisky sat out the first quarter of the season, but took every offensive snap for each of the last three quarters. Let’s see how he progressed through those.

Usage

First, I want to point out that Trubisky was tasked with doing more in each quarter.

In his first 4 games, Trubisky had the ball in his hands on only 26.5 plays per game. Coaches tried to minimize what he had to do, which was why more plays featured handoffs and fewer featured him ending the play with a pass attempt, sack, or run.

In Trubisky’s 5th-8th games, that number increased to 34.3 plays per game, and it took another jump to 39.8 plays per game in the last four games.

For the 32 qualified passers in the NFL this year (224 or more pass attempts), the mean and median were both 38.2 pass attempts, meaning Trubisky was being given as much responsibility (in terms of plays per game) as an average quarterback by the end of the season. This clearly shows that coaches were willing to put more responsibility on Trubisky’s shoulders as the season wore on, which is a good sign.

Efficiency

Now let’s see what Trubisky did with those increasing workloads. The table below shows basic efficiency data for the three quarters of the season that Trubisky played, as well as the NFL average (based on full passing stats for all 32 teams) and median NFL value (average of 16th and 17th best in that category of the 32 qualified passers). All data is from the excellent Game Play Finder at Pro Football Reference.

Here we can clearly see that, by and large, Trubisky improved statistically as the season wore on and his workload increased. That’s a very good sign. Increasing your workload and improving your efficiency is a difficult combination to achieve.

And now for a brief look at a few specific points I’d like to highlight:

Completion percentage is where you see the clearest sign of growth. Completing less than half of your passes, like Trubisky did in his first 4 starts, is simply not tenable. That’s Tim Tebow and Caleb Hanie territory. Trubisky quickly fixed that after the bye, and it wasn’t a problem going forward.

The yards per attempt was never a huge problem, though it also improved late in the season. Again, Trubisky was performing at or above average by the last quarter of the season, which is fantastic to see for a rookie quarterback working with sub-par weapons.

Likewise, interceptions were never really a problem for Trubisky. I’m not focusing on the slight differences between quarters, as those can bounce a bit due to the small number of interceptions (he had 2, 2, and 3 in the three quarters). Trubisky’s interception percentage was consistently right around NFL average, which is good to see for a rookie.

Those are 3 of the 4 variables that go into determining passer rating, and Trubisky performed at or above average in all of them for basically the last 8 games of the season, and especially the last 4. Yet his passer rating was consistently below average. That must mean he didn’t do so well in the last variable-touchdown percentage-and indeed, that one is consistently low. Trubisky only threw 7 touchdowns in 330 pass attempts, but that’s quite normal for young quarterbacks. The only qualified QB with a lower touchdown rate than Trubisky was fellow rookie CJ Beathard, and the rest of the bottom 5 were all first-time starters (DeShone Kizer, Jacoby Brissett, Brett Hundley).

So that’s the main statistical challenge for Trubisky going forward: figure out how to throw more touchdowns without throwing more interceptions. One advantage Trubisky has over some of his fellow young QBs is that they have to figure out how to throw more touchdowns and fewer interceptions. It’s not as simple as to say “throw more touchdowns,” there’s a lot more that goes into it than that, but statistically speaking that’s the area where you would hope to see the most improvement from Trubisky in 2018. And there’s recent context for that happening. 2017 sophomores Carson Wentz and Jared Goff both saw their touchdown percentage more than double from their rookie to sophomore seasons, while their interception rates stayed the same or decreased.

Passer Rating

Now for a brief comment on passer rating. Before the 2017 season, I found that, historically speaking, rookie QBs drafted in the first round are likely to be good if their passer rating is within 10 points of the median qualified passer. Trubisky’s overall passer rating was 77.5, 11.7 points lower than the median and thus just out of that range. This is basically due to the low completion percentage in those first 4 games, but alas, only 3 out of 11 quarterbacks who were outside of that 10 point range panned out. The Bears have to hope Trubisky bucks the odds a bit there. For what it’s worth, I think he will, and I think the improvements he made in the final 8 games help support that belief. Maybe later this offseason I’ll do a study looking at improvement through the rookie season for QBs from that sample.

Sacks

Finally, a comment on sacks. The rate at which Trubisky was sacked dropped throughout every quarter, but still remained above league average. I’m not worried about that. As I noted earlier, that was largely driven by a high sack percentage on 3rd and 4th down, when the Bears were consistently behind the chains and he had to wait for sub-par receivers to work open down the field. His 1st and 2nd down sack rates were in line with Chicago’s 2016 rates in the same situations, and that offense was better than average at avoiding sacks.

It’s also worth considering that maybe Trubisky got sacked a lot in part because he’s a rookie, and I’m sure this contributes some as well. For what it’s worth, Lester Wiltfong of Windy City Gridiron does a film breakdown of every sack and assigns blame for who was responsible, and he blamed Trubisky for 4 sacks this year (all of which came in his first 8 games). Bears quarterbacks were blamed for 8 sacks in 2016, 3.5 in 2015, 4 in 2014, and 7 in 2013, so Trubisky’s 4 in 12 games this year is not out of line with the norm.

TL;DR

Here’s the nice short summary for those of you who don’t like wading through a bunch of numbers. As the season went on, Trubisky had the ball in his hands more, and he responded by generally getting more efficient. The one area where he didn’t improve was that he didn’t throw many touchdowns, but this is common for a rookie QB, and everywhere else he was statistically at or above the league average by his final 4 games. Trubisky was also sacked way too much, but that got better as the season went on and was mostly not his fault.

What are your thoughts on Trubisky’s growth throughout his rookie season? Let me know in the comments below.