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Running Back Injury Risks

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by Mike Horn, Staff Writer

Published, 8/16/13

Everybody wants a stud running back this year, but at some point in a draft or auction, every owner has to consider taking or buying Calvin Johnson instead of one of the top RBs. The question then is, what to do for an RB1?

There are lots of possibilities, but each has his drawbacks: Maurice Jones-Drew coming on an injury and with questionable QBs, Chris Johnson always playing but never consistently and with his own QB question mark, Lamar Miller, but he hasn’t done anything yet and his line may be bad, etc. Another back to consider is DeMarco Murray. He does seem to get hurt a lot and his line is shaky, but how many eight-man boxes is he going to see? Murray has missed 9 games in his 1st 2 seasons – or to look at it from the other perspective, he has played 23 times. Does that tell us he’s more likely to miss games in his 3rd year?
 
I looked at how many games every RB since 1988 played in their 1st two seasons and then how many they played in Year 3. In order to narrow it down to backs who saw significant playing time, I limited the sample to RBs who averaged over 10 carries per game in each of their 1st two years (Murray averaged 12.6 and 16.1 carries per game).
 
Trivia question: Who are the other RBs who played their 1st two seasons in 2011-2012 who averaged over 10 carries per game in each of those years?
 
That gave me 66 RBs. I broke them into groups: those who played every game, those who missed a game or two each year, those who missed a few games each year on average, etc. The results are in the table below. For example, 18 of these RBs played all 32 games. In their third year (Y3), they averaged 13.7 games played. Six played all 16 games in their 3rd season, which was 33% of the 18 RBs in the group as a whole. Murray would be in the 22-25 games played group (highlighted in yellow):

1st 2 Seasons
# of RBs
Avg Games in Y3
# Playing 16G in Y3
% Playing 16G in Y3
32 games
18
13.7
6
33%
29-31 games
22
13.2
7
32%
26-28 games
17
10.9
2
12%
22-25 games
4
13.5
1
25%
16-21 games
4
11.3
1
25%
<16 games
1
9.0
0
0%
Total
66
12.6
17
26%

You can see that it doesn’t look like Murray is any more likely to play fewer – or more - games in 2013 than a typical young RB, even one who played every game his 1st two years. Of course, he’s in a very small sample, and I can slice the data differently to make the sample bigger and him look worse:

1st 2 Seasons
# of RBs
Avg Games in Y3
# Playing 16G in Y3
% Playing 16G in Y3
32 games
18
13.7
6
33%
29-31 games
22
13.2
7
32%
<31 games
26
11.3
4
15%
Total
66
12.6
17
26%

From the 2nd table, it looks like Murray is likely to play a couple of games fewer than an RB who missed almost no time in his 1st two seasons, and he is only about half as likely to play all 16 games.
 
Now even those three groups are still small. I can make them bigger by going back further than 1988, but then I run into the strike years between 1978 and 1987 when the NFL didn’t play a full 16-game schedule. Prior to 1978, the league played 14 games a year. So to account for those differences, I had to pro rate or adjust the games played to a 16 game schedule. So 9 games played in 1981 equals 16 adjusted games played, as does 14 games in 1977. But 8 games played in 1981 equates to 14.2 adjusted games (8/9*16) but 8 games played in 1977 is only 9.1 adjusted games (8/14*16). Again, all RBs had to average at least 10 carries per game in each of their 1st two years.

1st 2 Seasons
# of RBs
Avg Games in Y3
# Playing 16G in Y3
% Playing 16G in Y3
32 games
30
14.1
12
40%
29-31 games
41
13.7
14
34%
26-28 games
21
11.3
3
14%
22-25 games
10
13.7
3
30%
16-21 games
7
12.1
2
29%
<16 games
2
12.5
1
50%
Total
111
13.2
35
32%

The samples still aren’t huge, and again, in this look at the data, Murray would be expected to play 13.7 games in 2013, about the same as any back – maybe half a game fewer than an RB who played at 32 times his 1st two years. He might also be a little less likely to play every game in the coming year than a back who already had a track record of playing every week.
 
Again, if I slice the data differently, Murray looks worse.

1st 2 Seasons
# of RBs
Avg Games in Y3
# Playing 16G in Y3
% Playing 16G in Y3
32 games
30
14.1
12
40%
29-31 games
41
13.7
14
34%
<31 games
40
12.1
9
23%
Total
111
13.2
35
32%

I’m not sure how valid it is to compare a current RB to one playing a shorter schedule. It gets bigger groups within the overall sample, but I think there is a big difference playing all 16 games than playing a 9-game season – or even a 14-game year.
 
So based solely on how many games he has played so far, and depending on which data set you choose to believe, Murray can be expected to play 11-14 games this season versus 13-14 games from a back of more proven durability. It may be no difference or a couple of games worth.
 
An interesting observation is that an RB who played between 26-28 games the past two years (that is, who played a little more than Murray) may actually be expected to play fewer games than both Murray and the RBs who appeared in almost every game. I suspect this is just an anomaly in the small sample, but it’s there.
 
Now there are other arguments to be made about Murray’s durability – he had a history of injury in college. But missing several games in his first two NFL years would only appear to make him slightly more injury-prone going into his 3rd year than his peers.
 
Trivia answer: there are none. Murray is the only back who played his 1st two seasons in 2011 and 2012 and averaged 10 rushes per game in each season. So how durable are those other guys?

 

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