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Age and the NFL Draft

In yesterday’s Wall Street Journal, Kevin Clark noted that the Eagles targeted college graduates in the 2014 NFL draft. Six of the seven players selected by Philadelphia are on track to get their degrees before entering the NFL, which is important to Chip Kelly.

Kelly said a degree is more than proof of intelligence. “It’s also, what is their commitment?” he said. “They set goals out for themselves and can they follow through for it? A lot of people can tell you they want to do this, this and this. But look at their accomplishments.”

Kelly’s quote has a certain air of truth to it, but is it verifiable? Do players with college degrees turn out to be better pros than players who don’t obtain their degrees? Unfortunately, I don’t have historical data on whether players graduated college before entering the pros. So this post can’t and won’t answer that question.

But we do have player age for all NFL players, subject to a big caveat1 So here’s what I did:

1) Record the top 250 players selected in each draft from 1990 to 2009.

2) For each of those 5,000 players, calculate their Career AV in their first five years.

3) Create an expected AV curve for players by draft slot, which mirrors the myriad of other draft curves I’ve created.

av thru 5 years 1990 2009

In that chart, the average AV produced by each draft slot is in blue; the red line represents a smoothed curve. For the remainder of this post, the expected AV based on draft position reflects the red line.

4) Calculate the age as of September 1st of each class year for each prospect.

5) Run a regression using age and expected AV based on draft position to predict actual AV.

The result?

Actual AV = 34.7 + 0.91*DraftAV – 1.4*Age

The key part is at the end of the formula: for every year of age, a player’s expected AV in his first five seasons …. decreases.2 In other words, to the extent age serves as a proxy for college graduates, Kelly’s hypothesis isn’t just not true, it’s counterproductive. Youth appears to be undervalued in the NFL draft.3

After eliminating the players who never made it to the NFL, that left 4,234 players in my sample.  The average age of those players on 9/1 of the year in which they were drafted was 23.1 years. By far, the player who most overachieved relative to draft position was Terrell Davis, who was 22.8 years old on September 1st of 1995, the year he was drafted. Davis actually graduated from Georgia, so he’s an example of age not necessarily being a great proxy for earning a degree. Next on the list of overachievers was Ray Rice (21.6), Emmitt Smith (21.3), Zach Thomas (23.1), and Patrick Willis (22.6). Thomas and Willis were four-year players, while Rice and Smith left early.

Of course, you can’t get too much from isolated examples. And while the regression results are conclusive, they’re also a bit abstract. So here’s what I did next.

The number 4,324 is evenly divisible by 23, which means we can group our draftees into 188-player groups. I sorted that list of players from biggest overachivers (Davis, Rice, Smith… at 1, 2, 3…) to biggest underachievers (Charles Rogers at 4,322, Ryan Leaf at 4,323, and Akili Smith at 4,324). So Group 1 has the biggest overachievers, Group 2 has the next 188 best overachivers, Group 3 has the 188 best overachievers after them, and so on, while Group 23 has the 188 worst underachievers (and Group 22 has the 2nd worst set of 188 underachievers). Then, I calculated the average September 1st age of each group:

age draft 1990 2009

As you can see, the average age of the biggest overachievers was 22.8; that’s the youngest average age of any of our 23 groups.  The next three youngest groups are groups 2, 3, and 4; in other words, the biggest overachievers are the youngest players, and the relationship is pretty clear. Using age as a proxy for the binary “did he earn a degree” category is tricky, but the analysis here is clear that young players are undervalued.

One last interesting note. If you look at the far right of the graph, you see that the curve begins to slope downwards. This means the biggest bust are pretty young, too (although still older than Groups 1, 2, 3, or 4).  Evaluating younger players is probably trickier: not only is less tape likely available, but the projection of a player’s physical projection is trickier, too.

Players within 3 months of 21.5 years of age on 9/1/XX represent the most undervalued group in the study. There were 133 of those players, and on average, they overachieved by 5.3 points of AV.  Players within three months on either side of 21.0, 22.0, 22.5, and 23.0 produced about 1.5 more points of AV than we would expect based on their draft position. As you would expect, the standard deviations were higher there, too.  But it seems the risk is certainly worth it when it comes to drafting young players. Although that doesn’t appear to be the case when it comes to quarterbacks.4

  1. Unfortunately, we do not have such data on players who were drafted but did not make it to the NFL. This is a potentially serious issue with trying to analyze Kelly’s claim: if a non-graduate was selected in the draft but because of his “lack of follow through” he fails to even make a roster, he would be a shining example of Kelly’s claim but would be ignored in this study.. That’s a problem, but there’s no way around it. []
  2. Note: The R^2 is 0.34, which just means you can’t guarantee how good a player will be based solely on his age and draft position. The p-values associated with both age and draft value, however, are statistically significant at every level. []
  3. And arguably is even undervalued by this method, as — all else being equal — we would expect a 23-year-old player to produce more value in his first five years than a 21-year-old player. Of course, the issue regarding players who can’t even make it to the NFL remains. []
  4. I used this method to test whether quarterbacks were undervalued by AV. The regression results were inconclusive; the coefficient on age was -1.6, but the p-value was only 0.12 (sample size of 204). The biggest reason for the differing results, I suppose, is that AV is not the ideal way to measure quarterbacks. []

{ 27 comments… add one }

  • James May 22, 2014, 7:58 am

    Any relationship between age and draft order? Players picked early are most likely to bust, and picked later overachieve simply because of their draft slot peers.

    I can also see some players who are in college for 4-5 years and use up all of their eligibility aren’t as good players, otherwise they (probably) would have gone pro sooner to get a paycheck.

    • Chase Stuart May 22, 2014, 8:52 am

      I don’t recall the relationship between age and draft order, although I don’t think your other concern is too significant. Players picked early aren’t more likely to “bust” here because every player is graded against expectation for his draft value. So we are already taking quality into account by looking at AV over expectation and not just AV.

      Regarding your second point, well, that’s the thing Chip Kelly was arguing against.

      • James May 23, 2014, 11:24 am

        I was thinking more about magnitude than likelihood – a player drafted late like Terrell Davis can overachieve by a larger amount than a player drafted early because their baselines are so different; same for a player taken early can bust ‘harder’ because more is expected of them. I have no idea if that would make a difference though.

  • dgreen May 22, 2014, 8:44 am

    Q: Why does a 21 year old enter the draft?
    A: Because he’s awesome and already has a high draft value.

    Q: Why does a 21 year old not enter the draft and wait until he is 23?
    A: Because he’s not quite so awesome and wants to improve his draft stock.

    In other words, younger players are going to appear to be better picks because they are elites who don’t gain as much by staying in college and waiting until they are 23. The data for younger players is going to be biased towards the better talents. The data for older players is going to be biased towards guys who simply ran out of college eligibility.

    That’s my theory at least. It just seems like football is different than other sports when it comes to age, or that’s what we’ve been told. Baseball and Hockey love the younger guys because they have minor leagues. Football, with their smaller rosters and no minor league, need each guy who makes the team to contribute. Not sure how basketball fits into this. There was obviously a run on high schoolers for a while. Basketball seems to be ok letting a guy sit at the end of the bench for a year or two without contributing if he’s not ready.

    Just curious, how many players in your sample of 4,324 were in each age group? Maybe break it down by half years (21.0-21.4, 21.5-21.9, 22.0-22.4, etc.)?

    • Chase Stuart May 22, 2014, 8:54 am

      I’m not sure I follow your theory. Perhaps I have done a bad job of making this clear, but I’m controlling for draft position in this analysis. If younger players are better talents, they’d be getting picked earlier, but this study indicates that they should go even earlier.

      • Nate May 22, 2014, 9:22 am

        It makes sense. Assuming the average college starter is 20-22 years old (I do not have any real data on that), and Player A and Player B put up the same stats at the same position against that competition, how could one differentiate which player is more talented/better? If Player A is 19 years old, and Player B is 23, then it stands to reason that the younger player (A in this hypothetical situation) had a much more impressive season. Player A was beating competition that is older, more experienced, and more mature than he is; meanwhile, Player B did the same thing, but against competition that was younger, less experienced, and less mature than he is. Assuming that each put up an identical and “draftable” stat line, Player A looks like he might be a future elite NFL player, while Player B looks like an NFL “bust.”

        • Chase Stuart May 22, 2014, 9:51 am

          But under your scenario, Player A would get drafted much earlier than Player B, right? Well, if NFL teams were properly valuing age, that is.

          • Nate May 22, 2014, 10:22 am

            Player A SHOULD get drafted earlier, at least. What I was saying made sense was your article’s conclusion, and your response to dgreen. It is intuitive that, all else being equal, the younger player is a vastly superior prospect, if the stat lines suggest equal talents; since he was beating older players, and the other player was beating younger players.

            • Chase Stuart May 22, 2014, 12:24 pm

              Right. It kind of blows my mind, though, that something as obvious as age wouldn’t be factored in. One question asked on Twitter was whether that trend still exists: it’s possible (likely?) that this inefficiency will not appear in drafts from 2010-20xx.

              • Matt May 22, 2014, 12:32 pm

                Age may have been improperly valued in the first round because the rookie contracts were so big. Teams may have been scared to give a younger player such a large immediate contract, and may have picked a “safer, more mature” prospect. This would push talented younger players lower in the draft, so they would outperform relative to their draft status. Whether or not teams actually were doing this in their draft process? Who knows.

  • Sam May 22, 2014, 11:27 am

    Quick correction: you write “As you can see, the average age of the biggest underachievers was 22.8; that’s the youngest average age of any of our 23 groups. The next three youngest groups are groups 2, 3, and 4; in other words, the biggest overachievers are the youngest players, and the relationship is pretty clear.” I think you mean “overachievers” not “underachievers” in the first sentence.

    • Chase Stuart May 22, 2014, 12:24 pm

      Fixed!

  • Shattenjager May 22, 2014, 12:08 pm

    I’ve never understood why age is so often treated as unimportant in the NFL draft–it seems to be a major consideration in every other sport (Read Keith Law’s analyses for baseball–he brings up small differences in age often. And Law isn’t the type to say something matters for no reason.), but it’s largely absent from football draft analysis.

    One thing that bothers me about Kelly’s quote is that he seems to be assuming that everyone goes to college with the goal of earning a degree. I’m betting that for many players who end up in the NFL, that was never the goal of college. He’s using the college degree as a proxy for intelligence and “follow through,” but I’m not sure it really says that much about either.

    • Chase Stuart May 22, 2014, 12:25 pm

      Agreed on both points. I also wouldn’t put it past Kelly to be using some misdirection in the media, too.

      Because of my affiliation with all the baseball reference guys, the importance of age has been pounded into my brain. But I agree football analysts tend to ignore age much more than they should.

      • Shattenjager May 22, 2014, 12:42 pm

        A football coach not being totally honest with the media? That is a shocking and outrageous suggestion, Chase!

        Honestly, football analysts tend to pay less attention to age than they should even after players are in the league. Just as a couple of examples, every article about the personification of baseball greatness that is Mike Trout talks about his age, but your John Elway article is one of very few I can remember that pointed out how old he was to be producing at a high level at the tail end of his career.

    • Richie May 22, 2014, 2:46 pm

      I’m betting that for many players who end up in the NFL, that was never the goal of college.

      This was my first thought as well. In fact, it’s possible that a guy who graduates from college is not making football a high enough priority. [This is judging humans from the standpoint of developing the best NFL player, not developing the best human being.]

  • Nate May 22, 2014, 12:49 pm

    Have you checked out the new Playmaker Score from Football Outsiders (which I put together)? I found that underclassman status was a statistically significant factor in success, even after controlling for projected draft position (I haven’t run the regression, but I’m betting that it would come up significant even if actual draft position was used).

    Those findings seem to corroborate your analysis, and futher undermine Kelly’s position (at least to wide receivers), especially because looking at underclassmen status is as close to looking at the genuine article without combing the records of various colleges and universities.

  • Thunderlips May 22, 2014, 1:44 pm

    Ages of the Eagles draft picks this year:

    1 (26) – Marcus Smith, OLB, Louisville – 22
    2 (42) – Jordan Matthews, WR, Vanderbilt – 21
    3 (86) – Josh Huff, WR, Oregon – 22
    4 (101) – Jaylen Watkins, CB, Florida – 21
    5 (141) – Taylor Hart, DE, Oregon – 23
    5 (162) – Ed Reynolds, S, Stanford – 22
    7 (224) – Beau Allen, NT, Wisconsin – 22

    Young guys with diplomas. Win-win.

  • Richie May 22, 2014, 2:40 pm

    What does this mean?

    By far, the player who most overachieved relative to draft position was Terrell Davis, who was 22.8 years old on September 1st of 1995, the year he was drafted. Davis actually graduated from Georgia, so he’s an example of age not necessarily being a great proxy for earning a degree. </em?

    If Davis was 22 when he entered the NFL, wouldn't that be the expected age for a player who graduated from college?

    • James May 23, 2014, 11:27 am

      “The average age of those players on 9/1 of the year in which they were drafted was 23.1 years.”

      So Davis was a year younger than the average player, yet had graduated, when you would expect older players to be more likely to have graduated.

      My guess with 23 being the average age is due to redshirt years, so lots of players can stay in college for 5 years.

      • Richie May 23, 2014, 12:19 pm

        Davis would only be 0.3 years younger, not a year. But that’s the closest he could be to the average of the other players. If Davis came out a year earlier, he would have been 21.8 years old. A year later and he would have been 23.8.

  • mrh May 22, 2014, 2:49 pm

    I don’t write for them so I don’t feel bad plugging them, but the guys over at RotoViz have been beating the age drum for quite a while.

  • Richie May 22, 2014, 2:50 pm

    I think there is another factor that might run counter to Kelly’s statement. Younger players should provide more years of value (on average) before hitting their decline phase. So, theoretically, if you draft an underclassmen, you might get an extra year from his career than a guy who graduates. Or (gasp) from a guy who redshirted and graduated (spending 5 years in college).

  • Andrew May 22, 2014, 5:09 pm

    Finally someone has mentioned this. Age is always seemed as a threat in the work place then there is the whiff of paternalism in the “black” sports in football and basketball that is a factor in evaluation perceptions. Winston is perceived as immature. In my opinion, if had the texans pick, I would have drafted him if I was allowed to. Maturity has some validity but talent is talent. I want to see a high school player in the NFL. Have you guys seen the sizes of these players? Clowney seemed like the kid who was 15 in the sixth grade at the high school and college level. Had an off year and now he perceived differently. Maybe he was limiting his risk of injury when he “took plays off”. Looking at him avoiding combine workouts…dude has either some great advisors or some amazing foresight.

  • Michael May 22, 2014, 5:36 pm

    The biggest age difference between any of your groups is 6 months. This reminded me of a study done by researchers on the birth month of NHL players. They found that 3rd and 4th quarter birthdays correlated to longer, more productive careers, which contradicted NHL team’s tendencies to select players born in 1st and 2nd quarters. Your data makes me think that the difference in overachievers and underachievers may have a similar correlation as the NHL study.

    For anyone interested, the article was published in Plos One so it’s free to read online, and the title is Born at the Wrong Time: Selection Bias in the NHL Draft.

  • icdogg May 26, 2014, 2:40 pm

    Better players are more likely to make themselves available for the draft when they are younger, so of course you are going to get that relationship.

    If you have a high draft pick and you’re drafting for the top players with the most upside, you are usually going to draft one of the younger players. Chip didn’t have one of those top picks, so he wants guys who have experience playing in the same kind of roles that he is going to have them play in. He wants, for example, a 3-4 defensive end who has actually played 3-4 defensive end, so they are more ready from the start.

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