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Understanding 2021 Rookie Quarterbacks with Clustering and Bayesian Forecasting: How much confidence do we still have in Trevor Lawrence?

Jacksonville, Florida, USA; Jacksonville Jaguars quarterback Trevor Lawrence (16) screams during the second half against the Indianapolis Colts at TIAA Bank Field. Mandatory Credit: Matt Pendleton-USA TODAY Sports

After the 2020 season was a very good year for rookie quarterbacks on the field, the 2021 season marked the return of the usual growing pains for first-year signal-callers. Zach Wilson, Trevor Lawrence and Justin Fields struggled to produce, while Trey Lance hardly saw playing time behind Jimmy Garoppolo. Only Mac Jones enjoyed a strong start to his NFL career, making the postseason as a result.

Among the 31 quarterbacks who were on the field for 500 of their team’s snaps this year, the rookies rank 12th (Mac Jones), 23rd (Justin Fields), 26th (Trevor Lawrence), 28th (Zach Wilson) and 29th (Davis Mills) in PFF grade. Apart from Jones, this doesn’t sound very encouraging, but it’s often not fair to compare a rookie's performance to their experienced peers, as the average first-year quarterback increases their production by almost a standard deviation from Year 1 to Year 2.

Hence, we will look at how the 2021 rookie quarterbacks stack up among first-year signal-callers from the past to get a better understanding of how to evaluate their seasons. We will follow last year’s template and look at the quarterbacks from three different angles:

  1. Performance in stable and unstable metrics
  2. Quarterback clustering
  3. Estimating the distribution of future outcomes 
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Looking at different metrics

PFF's database contains thousands of data points, but some might be less interesting to look at for rookie quarterbacks than others. Last year, we examined some of our stats for rookie quarterbacks and determined how each statistic in the rookie season correlates to the same statistic in future years.

We ended up looking at the following set of metrics, some of which are stable and some of which are more unstable for the future. A higher R-squared value means the metric is more stable going forward.

Stable metrics Unstable metrics
Metric R^2 Metric R^2
Success rate (EPA > 0) 0.19 EPA/play 0.13
PFF grade 0.20 Net yards per attempt 0.09
Positively graded play % 0.22 Big-time throw % 0.10
Negatively graded play % 0.28 Sack rate 0.04
Turnover-worthy play % 0.20 % of throws behind the line of scrimmage 0.13
Scramble rate 0.60 % of plays resulting in deep completions 0.06
Avg. depth of target 0.22 % of yards coming from deep throws 0.00
% of throws beyond the sticks 0.34 First down rate 0.10
Time to throw 0.45

Here is how each how the 2021 rookie quarterbacks (minus Lance, who didn't play enough snaps) rank in the stable metrics among rookies since 2006:

Metric Percentile
Jones Fields Lawrence Mills Wilson
Success rate (EPA > 0) 97 59 77 53 13
PFF grade 84 64 31 25 14
Positively graded play % 63 69 27 14 23
Negatively graded play % 87 23 50 64 6
Turnover-worthy play % (High = fewer turnovers) 84 66 67 55 69
Scramble rate 17 98 55 36 41
Avg. depth of target 31 86 34 25 36
% of throws beyond the sticks 70 55 34 31 22
Time to throw (High = shorter) 80 9 33 81 14

And here is how they rank in the unstable metrics among rookies since 2006:

Metric Percentile
Jones Fields Lawrence Mills Wilson
EPA/play 84 17 45 27 14
Net yards per attempt 83 38 27 45 17
Big-time throw % 64 83 34 45 8
First down rate 83 38 34 25 14
Sack rate 80 5 83 44 6
% of throws behind line of scrimmage (High = lower %) 16 92 36 22 50
% of plays resulting in deep completions 47 50 23 67 20

Quarterback Clustering

We will use a clustering algorithm to classify and visualize statistical profiles for the rookies from both a performance and stylistic standpoint. The goal of quarterback clustering is to reduce the complexity of all the information we have about quarterbacks, namely the metrics occurring in the tables above.

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