Can Justin Fields Upgrade Chicago’s QB Performance in 2021?

Recently, I looked at Andy Dalton and found that he is not likely going to improve on the production the Bears got from their QBs in 2020. That means any improvement in the QB room likely has to come from rookie Justin Fields.

This is a more difficult projection to make because Fields doesn’t have years of NFL production to look at for an apples-to-apples comparison like I did with Dalton. Instead, I’m going to look at all rookies drafted in the last 10 years (2011-20 drafts) who attempted at least 300 passes in their rookie NFL season, with the idea being they played the majority of the year. This gives a sample size of 29 QBs; how many of them performed better than Chicago’s QBs in 2020?

The Setup

To do this comparison, I’m going to look at 3 stats, which I want to briefly explain here:

Yards per attempt + (Y/A)+. Yards per attempt is a simple enough metric, but the + indicates it is adjusted for era. Since this is comparing QBs over a 10 year sample, and league-wide yards/attempt has fluctuated year-by-year, this scales them all accordingly. 100 is a league average mark, anything higher is better and lower is worse.
Adjusted net yards per attempt + (ANY/A+). This takes yards/attempt and factors in touchdowns, interceptions, and sacks, and then scales according to league averages that year. A full explanation of the formula for adjusted net yards/attempt (which is from Pro Football Reference, just like Y/A+) can be seen here. The scaling is the same as Y/A+ above; 100 is average, and higher is better.
Expected Points added (EPA/Dropback). This attempts to account for the value of each individual play by comparing expected points on the drive (based on down, distance, and field location) at the start and finish of a play. Generally speaking, higher values here indicate that QB’s team is expected to score more points over the course of the season. A more detailed explanation can be found here. EPA data is pulled from this website.

The idea here is simple enough: how many of the 29 rookie QBs in the last 10 years with 300+ pass attempts have outperformed Chicago’s QBs from 2020? I also threw Andy Dalton’s 2020 season in just as a point of reference. Full data can be viewed here.

Results

The table below shows how the Bears did in all 3 stats in 2020, how Andy Dalton did in all 3 stats in 2020, the average for all 29 rookies in the sample, and the number of rookies who outperformed the better of the 2020 Bears/2020 Dalton in each stat.

A few thoughts:

First, notice how similar Dalton’s 2020 production was to Chicago’s QBs. This reinforces the earlier article that Dalton doesn’t really provide an upgrade to the 2020 combination of Mitchell Trubisky and Nick Foles.
There were a good number of rookies who upgraded Chicago’s 2020 QBs and Dalton. Over 2/3 (20 of 29) moved the ball through the air more efficiently (as evidenced by Y/A+), over 1/2 (16 of 29) were more efficient passers overall (as evidenced by ANY/A+), and over 1/3 (11 of 29) did a better job of helping their team score points (as evidenced by EPA/dropback).
The lower number of QBs improving the 2020 veterans for ANY/A+ and EPA/dropback is understandable. Both ANY/A+ and EPA/dropback are going to factor in touchdowns, interceptions, and sacks. Rookies generally have a low TD rate, and that proves true here too; only 3.8% of rookie passes were TD compared to 4.2% for both the 2020 Bears and 2020 Dalton. Interception rates were about the same, but we can also assume the rookies took more sacks than the 2020 veterans (though I didn’t look up the data to confirm this).

Conclusions

All in all, 11 of 29 QBs (more than 1 in 3) upgraded the 2020 veterans in all 3 stats, while 16 (more than half) were better in at least 2. Thus there’s a real chance that a rookie QB can step in right away and perform at a higher level than we expect from Andy Dalton in 2021.

Of course, there are no guarantees. About 1 in 4 of these QBs (8 of 29) were worse than the 2020 veterans in all three statistics, including some absolutely horrible results. Just look at these stat lines put up by rookie QBs drafted in the 1st round over the last decade:

Josh Rosen: 217/393 (55%) for 2278 yards (5.8 yards/attempt), 12 TD, 11 INT (corresponds to 72 Y/A+, 66 YPA/A+, -0.238 EPA/dropback)
Blaine Gabbert: 210/413 (51%) for 2214 yards (5.4 yards/attempt), 12 TD, 11 INT (corresponds to 65 Y/A+, 71 ANY/A+, -0.176 EPA/dropback)
DeShone Kizer: 255/476 (54%) for 2894 yards (6.1 yards/attempt), 11 TD, 22 INT (corresponds to 77 Y/A+, 67 ANY/A+, -0.102 EPA/dropback)
Blake Bortles: 280/475 (59%) for 2908 yards (6.1 yards/attempt), 11 TD, 17 INT (corresponds to 75 Y/A+, 69 ANY/A+, -0.091 EPA/dropback)

There’s certainly no guarantee that Justin Fields would be an immediate upgrade for Chicago in 2021. In fact, he may end up being a downgrade. But there’s also a real chance that he can provide a significant improvement, which is more than you can say for Andy Dalton. About 1/4 of rookie QBs were worse than what Chicago had in 2020, but about 1/4 of them were above league average in both Y/A+ and ANY/A+. Andy Dalton is not going to be a better than league average QB in 2021, but Justin Fields might.

Of course, the Bears need to keep a bigger picture in mind when considering what to do with Fields. He was drafted for the 2020s, not just 2021. They shouldn’t force him onto the field just because he’s their only chance at a QB upgrade, but if they think he’s ready, they should be willing to play him (I should also note that there is no evidence sitting a QB increases his ultimate career outcome). Fields is definitely Chicago’s best QB option long term, but he also offers their highest chance of getting quality QB play in 2021.