SITE NEWS: We are moving all of our site and company news into a single blog for Sports-Reference.com. We'll tag all PFR content, so you can quickly and easily find the content you want.

Also, our existing PFR blog rss feed will be redirected to the new site's feed.

Pro-Football-Reference.com » Sports Reference

For more from Chase and Jason, check out their work at Football Perspective and The Big Lead.

How many YPC will RB X average this year?

Posted by Chase Stuart on May 24, 2010

What is the most accurate way to project a running back's yards per carry average for next season? What does history say about how many yards per rush Chris Johnson, Steven Jackson and Michael Turner will average in 2010?

I ran a query using all RBs since 1988 who had at least 200 carries in Year N, at least 100 carries in Year N+1 and did not switch teams in between years (I didn't want to bias the sample by potentially eliminating running backs who struggled so much in Year N+1 that they failed to receive 200 carries). After doing so, I wrote and finished this blog post ... and then realized that my analysis was incorrect. Why? Because I hadn't realized that yards per carry averages have been rising over the past 20 seasons. The table below shows all carries and rushing yards by running backs in the NFL since the merger:

year   carries rshyd   ypc    5yearaverage
2009   12390   53114   4.29   4.19
2008   12473   52985   4.25   4.17
2007   12417   51695   4.16   4.16
2006   12694   53253   4.20   4.16
2005   12738   51826   4.07   4.13
2004   12747   53334   4.18   4.11
2003   12759   53351   4.18   4.05
2002   12105   50285   4.15   4.01
2001   11711   47300   4.04   3.98
2000   11688   46649   3.99   3.95
1999   11861   46144   3.89   3.95
1998   11967   47559   3.97   3.92
1997   12046   48231   4.00   3.91
1996   11966   46651   3.90   3.92
1995   11734   46585   3.97   3.93
1994   11213   42051   3.75   3.94
1993   11233   44064   3.92   3.97
1992   10774   43545   4.04   3.99
1991   10924   43255   3.96   3.96
1990   10975   44456   4.05   3.95
1989   11540   44984   3.90   3.97
1988   12060   48030   3.98   4.01
1987   11710   45842   3.91   4.03
1986   12180   47831   3.93   4.01
1985   12257   50873   4.15   4.03
1984   12518   50753   4.05   3.99
1983   12951   52954   4.09   3.98
1982    7078   27197   3.84   3.96
1981   13364   53741   4.02   3.96
1980   13147   52025   3.96   3.96
1979   13878   55486   4.00   3.96
1978   14861   58927   3.97   3.93
1977   13488   51920   3.85   3.94
1976   13330   53851   4.04   3.98
1975   12259   48428   3.95   3.96
1974   11517   44132   3.83   3.92
1973   11840   47673   4.03   
1972   11138   45081   4.05   
1971   10819   42863   3.96   
1970   10505   39111   3.72

In 1994, the average running back in the NFL averaged only 3.75 yards per carry; last year the average was over half a yard higher. That 1994 number was a really low outlier even in an era of low numbers; we may one day look back on 2009 as the high point for rushing prowess. Because of the changes in yards per carry averages, in order to do any meaningful YPC analysis across eras, we need to control for era. (As an aside, one could argue that the high YPC we see today is a direct result of the running back-by-committee trend that's taken over the NFL over the past few seasons; the data does not show, of course, that RBBC leads to higher YPC averages. It does appear that there's a correlation, but remember that RBBC was prevalent in the '70s and '80s, too. Personally, I think more teams following a RBBC approach probably has something to do with the higher averages we're seeing, but that's just my own opinion.)

There were 313 running backs who had at least 200 carries in a year since 1988 and then at least 100 carries for the same team in the next season. Barry Sanders had the two highest era-adjusted averages, with his 6.13 YPC average in 1997 being a mind-boggling 2.22 yards per carry greater than the average running back from '93 to '97; his 1994 season (5.69 YPC) came in at 1.74 YPC better than the trailing five-year average. At the other end of the spectrum? Eddie George, whose 2.98 YPC average in 2001 was a full yard below that of the average runner from 1997 to 2001.

I first ran a regression using just yards per carry in Year N as the input and yards per carry in Year N+1 as the output. The best fit equation is as follows, with YearN_Diff being the difference between the player's YPC average in Year N and the five-year trailing league average:

YPC_n+1 = =LgAvgYPC -0.04+0.43*(YrNDiff)

What's that mean? Assuming a league average of 4.20, that means we would have the following 2010 projections from the below 2009 averages:

2009	2010
3.3	3.8
3.4	3.8
3.5	3.9
3.6	3.9
3.7	3.9
3.8	4.0
3.9	4.0
4.0	4.1
4.1	4.1
4.2	4.2
4.3	4.2
4.4	4.2
4.5	4.3
4.6	4.3
4.7	4.4
4.8	4.4
4.9	4.5
5.0	4.5
5.1	4.5
5.2	4.6
5.3	4.6
5.4	4.7
5.5	4.7
5.6	4.8
5.7	4.8
5.8	4.8
5.9	4.9
6.0	4.9

Another way to think of this is that any starting running back's YPC projection next year should be roughly equivalent to about 3/7 of his YPC average last year and 4/7 of 4.2 yards per carry (i.e., the league average). If that doesn't seem very exciting to you, you might wonder if there's an easy way to improve that by adding more inputs.

I tried adding rushing attempts and rushing touchdowns to the regression, individually and jointly, and neither improved the formula. Same goes for age. There were three variables that did have slight correlations, although I'm slightly skeptical about each of them. I don't think there's a one size fits all approach to predicting yards per carry, but I can understand why, on average, these three variables are correlated with yards per carry. One was draft status (using my draft value chart for each draft slot as my input, instead of actual draft slot, since draft value does not fall at a linear rate). Of course, draft status is just a proxy for talent, and I'm not sure how useful that piece of information would be on a case by case basis. Receptions were positively correlated with yards per carry as well -- although I wonder if it's just been a recent coincidence that some of the best pass-catching backs have had some of the highest YPC averages. This could be a case where the correlation that does not necessarily having significant predictive value. The final variable that held predictive power was weight (which was more predictive than BMI). The lighter the player, the higher the projected yards per carry average; once again, it's plausible to conclude that this is just a case where that's how the historical data played out, and it won't be the case going forward. The best fit formula, using those three variables in addition to the Year N difference in yards per carry, was:

YPC_n+1 = = LgAvg + 0.90 +0.004*Draft+0.0045*Rec-0.0055*Wt+0.35*YrN_Diff

So what the heck does this mean? Well, for every 18 pounds of weight on a player, you should reduce his projected YPC by 0.1; the difference between a 200- and 236-pound running back, all else being equal, is about 0.2 projected YPC in Year N+1. Similarly, every 22 receptions a player has increases his expected YPC by about 0.1 YPC in the following season. And hearing the commissioner call your name first overall -- relative to him never calling your name at all -- increases your projected YPC in Year N+1 by about a quarter of a yard per carry. And with all of these extra things in the formula, the Year N yards per carry variable goes from making up about 42% of the future projection to about 35%, about a 16% drop.

Let's throw these all together to show the best fit projections for the 2010 season, looking at RBs who had at least 200 carries in '09 and have not yet switched teams this off-season:

Name year TM YPC REC DRAFT WEIGHT Proj
Chris Johnson 2009 TEN 5.60 50 33.2 195 4.87
Ray Rice 2009 BAL 5.27 78 22.8 195 4.84
DeAngelo Williams 2009 CAR 5.17 29 31.7 210 4.53
Frank Gore 2009 SFO 4.89 52 20.7 215 4.47
Maurice Jones-Drew 2009 JAX 4.46 53 21.7 205 4.38
Ricky Williams 2009 MIA 4.65 35 52.9 226 4.37
Jonathan Stewart 2009 CAR 5.13 18 40.9 235 4.36
Adrian Peterson 2009 MIN 4.41 43 48.7 217 4.35
Rashard Mendenhall 2009 PIT 4.58 25 33.7 210 4.31
Steven Jackson 2009 STL 4.38 50 33.2 229 4.25
Fred Jackson 2009 BUF 4.46 46 3.0 215 4.23
Cedric Benson 2009 CIN 4.16 17 55.8 222 4.14
Joseph Addai 2009 IND 3.78 51 30.4 210 4.14
Cadillac Williams 2009 TAM 3.90 29 52.9 217 4.12
Ryan Grant 2009 GNB 4.44 25 3.0 218 4.11
Marion Barber 2009 DAL 4.36 26 14.2 221 4.11
Knowshon Moreno 2009 DEN 3.83 28 41.9 217 4.06
Matt Forte 2009 CHI 3.60 57 25.6 221 4.02
Kevin Smith 2009 DET 3.44 40 20.9 210 3.93
LaDainian Tomlinson 2009 SDG 3.27 20 52.9 221 3.84
Brandon Jacobs 2009 NYG 3.73 18 14.0 256 3.66

Some quick thoughts:

  • Chris Johnson's projection still looks a little high to me, although he may be helped out by having a full year's worth of Vince Young in the backfield.
  • Ray Rice's 78 receptions give him a huge leg up in this projection system; I'd be skeptical of that.
  • Frank Gore averaged 4.9 yards per carry last season before the team drafted two offensive lineman in the first round. I think a lot of people will project huge numbers for him in 2010, and I can't say I blame them.
  • At some point, I don't think draft value carries a lot of weight. And I think Ryan Grant is well past that point.

This entry was posted on Monday, May 24th, 2010 at 7:40 am and is filed under Statgeekery. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.