I am going to approach the issue on a narrower level, by digging into the individual games database to see if there is evidence of a danger zone when it comes to rushing attempts, measured over a shorter period of time. In baseball, for example, pitch counts have become a common statistic, and Rany Jazerli and Keith Woolner of Baseball Prospectus developed a statistic known as Pitcher Abuse Points (PAP). Here is the question I will seek to answer: Is there a "rush count" in football that should be observed over the course of a game, or period of games, that should be observed to keep running backs healthy?
Two potential issues arise when looking for evidence of overuse. The first is whether high attempts increase the risk of injury serious enough to cause missed games. The second is whether high attempts reduce effectiveness/performance beyond what would be normally expected. And of course, these two issues can be related, as a severe injury could reduce a back's effectiveness/performance faster than normal, even after the back has "returned from injury."
For now, I am going to focus on the first issue (injury), by looking at games played. "Games played" is not a perfect measurement for injury, as players could also be benched, or be suspended. However, by limiting the players examined to those averaging over 15 carries a game over a period of time, we can be fairly certain that most games missed are due to injury, rather than coaching decisions.
Using the games database for the 1995-2006 regular seasons, I ran a sort of all running backs who (1) played in all 6 of their team's first 6 games; and (2) averaged 15.0 or more carries per game over that span (90 attempts or more total). I then sorted them by attempt totals, and looked at the average number of games played for the rest of the season.
Thus, if a player started off the season missing some games, or even worse, suffering a severe injury, they are not included in this particular study--they will be addressed later. By including only players who played in all games through the first six, the hope is that we are looking at players who are healthy. Or at least healthy enough to continue to play. There is nothing magical about my choice of a six game period. The main reason I chose it was because it was a small enough span to capture a good amount of players but also large enough to see the effect of workload over a group of games. It also left a nice, round, ten regular season games for each player, so the math on the average games played is easy. Here are the results:
# Attempts # Players Av GP, rest of year ============================================== 150 or more 9 7.9 138 to 149 24* 8.5 126 to 137 42** 9.2 114 to 125 46 9.2 102 to 113 54 8.5 90 to 101 37 9.1 * Lamar Smith, 2002, excluded because placed on leave due to a DUI. He missed last 5 games of season. **William Green, 2003, excluded due to missing last 9 games after league suspension =================================================
We see that the running backs peak, in terms of number of remaining games played, in the 114 to 137 carries range (19.0 to 22.9 attempts/game). The average number of games played dips on either side of this group. However, if we look at how the "138-149 attempts" and "150+ attempts" groups ("the high carry groups") are missing games compared to the lower attempt groups, a different pattern emerges.
Here are the percentage of players for each group who, due to injury, played in 50% or less of the remaining ten team games:
- 150 or more 2/9 22.2%
- 138 to 149 3/24 12.5%
- 126 to 137 2/42 4.8%
- 114 to 125 2/46 4.3%
- 102 to 113 5/54 9.3%
- 90 to 101 1/37 2.7%
The high carry groups show a significant increase in the percentage of players missing at least half of the remaining games. But still, we are talking about five players, and a couple of freak injuries could skew the data. So, I took a closer look at those 15 players who missed 50% or more of the remaining games. The players are presented in order of total attempts through the first six games, with attempts and remaining games missed (out of ten) listed. I have also discussed the nature of each injury, when it developed, and notable issues of immediate workload around the time injury, if they existed.
- Ricky Williams, 2000, age 23, 155 att, 6 games-- Williams broke an ankle in game 10 vs. CAR, ending his season. His workload was even higher right before the injury than it was through the first six. He averaged an astounding 29 attempts per game in the 5 games before the injury. Ricky had also missed 4 games in 1999 (rookie year).
- Edgerrin James, 2001, age 23, 151 att, 10 games-- James tore his knee on a stretch play to the outside, on his 27th carry in a week 7 game in KC, after games of 26 and 30 attempts the previous two weeks, following a week 4 bye.
- Priest Holmes, 2004, age 31, 148 att, 8 games-- Priest injured his knee in week 9 at TB, missed rest of season. Had 32 carries previous week, which was 3rd game out of previous 5 with more than 30 attempts.
- Robert Smith, 1996, age 24, 140 att, 8 games-- Smith had missed 7 games previous year. Had 3 games of 26+ attempts in the 6 games immediately prior to injury. Tore knee in game 8 vs. CHI on the 4th carry.
- Natrone Means, 1998, age 26, 139 att, 6 games-- Means (apparently worn out from playing with Ryan Leaf) suffered a season-ending foot injury early in week 11 vs. BAL. Had 27+ attempts in 3 of previous 5 games, including a game with 37 attempts. Had missed 11 games over previous 3 seasons to injury. Played in 7 more career games.
- Natrone Means, 1995, age 23, 133 att, 6 games-- Means suffered a groin injury on the 2nd carry of week 10, coming off a bye week. Means had only 1 game with less than 22 carries since week 1, including 26 the last game before the injury. Came back in week 16, but re-aggravated injury after 3 carries, and missed the final week as well.
- Duce Staley, 2004, age 29, 126 att, 6 games-- Staley had 25 carries in final game before suffering hamstring injury, his 2nd 25 carry game in 4 games. Missed 4 straight games, came back to play 3 of last 5, but only had 41 total attempts. He played in 6 more games after 2004 season.
- Chris Brown, 2004, age 23, 120 att, 5 games-- Chris Brown had 27 attempts in week 5 and a career high 32 attempts in week 8, before a week 9 bye, came back to have 20 attempts in week 10, then missed next 2 games with turf toe injury. Played in 2 more games, then missed final 3 with same injury. Had missed 5 games previous season with hamstring injury. Brown averaged 4.8 ypc in 2004, and has averaged 3.8 over the last few seasons, and was a non-factor at age 25 last season.
- James Jackson, 2001, age 25, 119 att, 5 games-- Jackson had 32 attempts in week 2, 26 in week 4, and 24 in week 6. Played two more games after week 7 bye week, before first injury. Suffered ankle injury that forced him to miss 2 games (weeks 10 and 12) and then suffered another season-ending ankle injury early in week 14 vs. JAC. Jackson had a total of 130 more rush attempts over next 4 seasons.
- Domanick (Davis) Williams, 2005, age 26, 113 att, 5 games--Davis had back to back games of 28 attempts in weeks 8 and 9, then missed next 2 games with a knee injury. Coming back for the then 1-win Texans, Davis had 13 attempts in week 12, then followed with a 3 game stretch of 25, 29 and 22 attempts, before missing the final 3 weeks with further injury to the same knee. Missed all of 2006 season due to same knee injury, questionable if he will ever play again.
- Jerome Bettis, 2001, age 29, 112 att, 5 games-- Bettis had 94 carries in the 4 games immediately prior to suffering groin injury in week 12, including 29 attempt game in week 9. Bettis missed rest of regular season, came back to try to play in the playoffs that year.
- Terry Allen, 1998, age 30, 111 att, 6 games-- Allen had already missed a full season to a knee injury earlier in career, and had missed 6 games previous season. Missed 6 games with ankle sprain.
- Priest Holmes, 2005, age 32, 105 att, 9 games-- Priest had missed 8 games previous year. No games higher than 22 attempts (week 1), as he was sharing carries with Larry Johnson. Injured neck against SD, on a hit from Shawne Merriman. Has not played since.
- Robert Smith, 1995, age 23, 104 att, 7 games-- Smith never had more than 20 attempts in a game before suffering an ankle injury that caused him to miss 7 of the last 9 games.
- Terry Allen, 2001, age 33, 99 att, 5 games -- See Terry Allen, 1998, above. Allen missed 5 games with a broken hand.
Three out of 33 players with at least 138 attempts through six games suffered a serious season ending injury (all three knee injuries) before the end of game 8. Only one out of 179 who had between 90 and 137 attempts were out for the season by game 8. That one was a 32 year old back with recent injury history, and the injury was a neck injury. Further, by my count, ten of the fifteen had games with 25 or attempts--and generally multiple games--in close proximity to the first injury. I will count James Jackson as questionable on this issue, as his injury came a little further removed from his highest workload games. Of the four who did not show any significant workload games prior to injury, three were of advanced running back age and had recent prior injury history. Only Robert Smith (1995) could be considered a younger running back who did not show a recent high workload near the time of injury onset.
The majority of running backs, though, survived the period of early heavy usage without suffering an immediate injury. 24 of those 28 running backs in the high carry groups that did survive immediate injury went on to finish the season with 15 or 16 games played. So, if they did not manifest a severe injury soon after the high workload period, it did not seem to have a lingering effect. Although I am not going to focus on performance, I did test to see if these backs were wearing down as a result of early workload. They were not. For backs who played in at least six more games, there was no correlation between early workload, and changes in yards per carry from those six games versus the rest of the season. In fact, the highest group showed a slight increase in ypc the rest of the year.
The success rate for the high carry groups in getting to the end of the season relatively unscathed, if they survived immediate injury, was comparable with their peer group of feature running backs in the 19.0 to 22.9 attempts per game. I also checked games played by backs in the high workload groups against prior workload history (measured by total career attempts divided by career games), raw career attempts totals, and age. Prior workload history did not matter either way--those injuries hit both high and low career workload backs. What mattered was the present workload. Age also showed no correlation, although the 25-27 age group performed better in this regard, and the games missed increased in both the younger and older groups.
Among the lower carry groups (those who had 113 or fewer attempts), the reason for decline in average games played is not serious injuries. These groups tend to have a higher number of aging backs, backs with recent injury concerns, or backs "playing through injury." As a result, a lot more of these backs are missing some games due to nagging injuries--missing a game here, two games there. Workload, in the short term, is indicative of good health, at least as of the time the running back is being subjected to those additional carries.
In the next post, I am going to examine the end of season and playoff workloads, and their effects on injury rates early the next season.
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