Tuesday, July 21, 2020

Published 9:28 PM by with 0 comment

How Bad Were Jameis Winston's 30 Interceptions in 2019?

In 2019, Jameis Winston threw 30 interceptions. That seems extremely high for a modern starting quarterback, so I wanted to see if it was the largest outlier ever.
Two obvious questions come to mind:
  • Was his total interception number a massive outlier compared with his peers?
  • Was his interception per pass attempt number a massive outlier compared with his peers?
First, what does 'compared with his peers' mean? I'm using the following algorithm:
  • take all starting quarterbacks in a season
  • filter down to ones with at least 200 pass attempts
  • calculate the average and standard deviation of their interception count
  • subtract each qbs interception count from the average that season, and divide by the standard deviation that season; the result is a measure of how much of an outlier his interceptions were that season
  • repeat for all seasons
  • repeat for 'interceptions per pass attempt'
As a quick example, imagine the average starting quarterback threw 18 interceptions in a season and the standard deviation was 4.2. If a quarterback threw 29 interceptions that season, his score would be (29 - 18)/(4.2), or 2.62. That player's interception count that season is 2.62 standard deviations above the average.

With that behind us, let's see the numbers. For total interception count, the worst season (compared with peers) was...

Brett Favre in 2005.

#2 by this metric was Jameis Winston in 2019. Rounding out the top 5 are Jay Cutler in 2009, and Vinny Testaverde in 1988 and 2000.

So Winston's 2019 was an outlier but wasn't the worst at least. What about the 'interceptions per pass attempt' metric?

By that one, Jameis Winston's 2019 season is 6th worst ever. 1-5 is Kerry Collins in 1997, Vinny Testaverde in 1988, Deshone Kizer in 2017, Mark Sanchez in 2009, and Brett Favre in 2008.

Also, to further clarify the 'compared with peers'...in 1988 Vinny Testaverde threw 1 interception every 13 passes while in 1997, Kerry Collins threw 1 interception every 18 passes. However, Collins ranks higher with this metric. This is because overall, QBs throw much fewer interceptions now than they did 30 years ago. To see this, here's a plot of the average interceptions per pass attempt among starting QBs each season:



An immediate question is 'why has this declined?' I don't have the data right now to analyze that (I'll hopefully do this in a future post), but I'd guess it's primarily due to throwing shorter routes. Screen passes and routes <10 yds downfield seem much more common now and those are much less likely to end in an interception.

Anyway...closing this out, Winston's 2019 season had a high number of interceptions, but it wasn't the largest historical outlier even when adjusting for peers.


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