EPA Production and Cap Value, Skill Positions

I've been playing around with the connection between player value and production, and I thought I'd post some interesting observations.

As a measure of production I used Expected Points Added (EPA)--actually EPA per game to account for injury shortened seasons. For the measure of player value, I used cap hit. Cap value is useful because it boils down the complexity of many NFL contracts into one number. It can be tricky, though, as many contracts can be quite uneven from year to year in terms of cap value. For cap management and player-incentive purposes a 4-yr/$40M will often diverge far from a steady $10M per year cap hit. To account for this, I averaged each players' per year cap hit for the full period ('06-'12) and plotted against each player's EPA/G. The purpose of doing this is to see what level of production teams expect per $1M of salary. Is there a solid connection between true production and salary?

There are assumptions and limitations inherent in this analysis. Player production is dependent on the abilities of their teammates. WRs and TEs rely on their QBs to get them the ball, and some will have better passers and some will have worse, and vice versa. RBs are dependent on their line and scheme. But over the league as a whole, these considerations would (ideally) balance out. Put simply, for every Larry Fitzgerald being victimized by the offense around him, there's a Brandon Lloyd benefitting from being on a great offense.

The chart below plots offense skill position production by annual average cap hit. Each position is color coded.

The trend lines show that the offensive skill positions have different connections between production and salary than others. The more diagonal the line, the stronger the connection. The order is QB, TE, WR, and RB. (Note: I set the minimum avg cap value to $500k and minimum game appearances to 7 per season to focus on the players meant to be starters. Raising the minimum cap value up through $2M doesn't change the general results above. Above that there are so few players that the results become spurious.)

This result points to how consistent a player's abilities can be assessed and predicted at each position. Perhaps QBs can be evaluated and assessed more accurately than the other positions.

It may also say something about how heavily dependent a position's production is on factors beyond his control. RB production may be so overwhelmingly dependent on line and scheme that a player's underlying ability is swamped.

Random factors may affect the positions in different ways. For instance, a few extra lost fumbles can erase an entire season's worth of production for a RB. Or perhaps injuries, which are largely random, affect positions in different ways.

The correlations are as follows:

QB 0.43
TE 0.28
WR 0.22
RB -0.03

All the correlation values are significant at the .01 level except for the RBs, which was not significant.

This is just a first cut, but I wanted to document things at this stage. Next, I'd like to eliminate all the seasons for which a player was under his rookie contract, leaving only the relatively free market of free agents in the data. As an aside, it's interesting to see how stark the pay differences are between the top QB picks like Ryan and Sanchez, who had their rookie contracts done prior to the new CBA, and more recent picks such as Luck, Griffin, and Newton. And if we didn't already know it, Russell Wilson appears to be quite the steal.

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9 Responses to “EPA Production and Cap Value, Skill Positions”

  1. Anonymous says:

    So, where is Tom Brady in this chart??

  2. Ian Simcox says:

    Wow, if you're a RB you're hoping your GM doesn't see this. If there's no correlation between what teams pay and the performance they get back, then you can pretty much stick anyone back there. Which is kind of what people think anyway, use the money to beef up your o-line. Behind a quality line, even I could rack up 4 yards per carry.

  3. Anonymous says:

    ^Rodgers too. There's one unlabeled blue dot between Vick and Favre, but both their EPAs are higher than that.

  4. James says:

    Brian, don't you need to add a constant to EPA per play to be able to do this analysis? A RB that provided 0 EPA over 300 carries is more valuable than one that provided 0 EPA over 30 carries.

    It's like the difference between Wins Above Average and Wins Above Replacement in baseball.

    Also, without removing the rookie contracts it's hard to see what this means. As you probably already know Chase has been working on the same topic over at footballperspective.com

  5. Drew Vogel says:

    I don't think any GM would be surprised at all. If anything this shows the limited value of EPA. I would have been stunned to read that RB salary had anything to do with EPA. The role of the RB has changed so much over the past decade. There's very few RBs considered as more than "closers" for their QB. Certainly the consensus view on Aaron Rodger's WPA trailing his EPA must be that the defense has let too many teams back into the game, partially because the Packers don't have a RB to keep the clock rolling and close out the game. In short: RBs are paid for WPA, not EPA. Why did you choose EPA instead of WPA?

    Have you considered tracking an additional stat that incorporates the shift in momentum? You could weight EPA by the time since the opponent's last score, or something similar. My intuition (probably wrong) is that this would correlate quite strongly with QB salaries. Brady, Rodgers, Peyton, now Flacco are all valued for their ability to "answer" when their opponent scores. It would probably have a negative correlation with RB salaries.

  6. Brian Burke says:

    James--that's a good point. It's tricky. If I use EPA/P that overvalues positions that are used less often than others. The constant would fix that.

  7. Anonymous says:

    What about Brady and Rodgers not being on your graph at all?

  8. Mike Filicicchia says:

    It seems like to accurately assess a player's value, you can't measure EPA/G, but rather "EPA/G above replacement". This will lower the QB's values since most back-up QB's can still outperform starting (and even elite) RB's in terms of EPA/G. This does not make them more valuable, however, and will give you a much more coherent and meaningful set of data.

  9. Two Scoops says:

    To me this indicates something might be slightly off with EPA. I generally agree with the conclusions, but Megatron/Fitz/AP types I think are able to provide significantly more value than their typical counterparts.

    It seems as if non-QBs max out at like 4 EPA/game. Is there a person in existence that would take Carson Palmer over Megatron? Maybe replacement level isn't being factored enough?

    RBs appear to cap at about 2 EPA/game. That just seems so little.

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