While one avenue for evaluating NFL injuries is to look at the sum of a team’s injury report, the number of players and total level of severity, another option would be to focus on positional analysis.

Theories abound that an injury at a certain position is more significant than at others. You may have comes across people maintaining if the center is out it’s a huge blow (“all those botched snaps lead to fumbles”), a hurt cornerback spells downfall (“teams have a hard enough time finding two good corners, let alone decent backups”), or of course the quarterback as all-important.

Opinion matters little to us though unless we have some statistical basis behind it. Our first challenge will be to investigate whether different positions do have different levels of effect on a team’s outlook for a given week.

The following table breaks out the injuries listed on the NFL’s official weekly Wednesday report for the 2001 regular season, and shows a team’s cover percentage with a player of a certain position and status on the report:

First some caveats: the data above reflects only one season of games, and so we are dealing with small sample sizes. In addition the 2001 season may differ in character from other years. Finally please note that whether a player is a starter is not considered.

Having issued the qualifiers, what stands out in the above is that, as might be expected, injuries to quarterbacks often lead to over-reaction. A team with a QB unlikely to play (doubtful or out status) covered the spread at a 63% clip in spite of this apparent “calamity.”

At the same time, a seriously hurt tackle, linebacker, cornerback or safety suggests some level of damage to a team’s chances against the line in the upcoming game. Most surprisingly, a kicker or punter with a “nagging” injury (pegging the player as probable or questionable) had a severe implication in 2001: the team only covered 29% of the time!

The next step could be to break out the numbers above to reflect whether a player was a starter or a reserve, but since reserves can often play key roles on special teams as well as being significant contributors to their position, we’re not enthused with that line. Instead, we’ll go another route and take a look at what happens when a team has two players or more with a serious injury level (“questionable” or worse) at a given position class. Since we’re dealing with small sample sizes to begin with, we’ll group offensive linemen, defensive linemen, and defensive backs together.

Now there were only three cases in 2001 where a team had two quarterbacks listed as questionable or worse, so don’t get too excited by the early results. About the only area of particular interest is when a team has two defensive backs questionable or worse, where the team covered only 40% of the time, and that’s over a seventy-six game sample. Teams with three DB’s in bad shape were only 34% against the line (and teams with three WR’s hurting were only 27%), so it does imply that depth can be a factor.

We expected the offensive line to be a more telling zone, since much is made of the importance of a team’s line playing together over time. It could be a myth, it could be our sample is too small, or it could be the line is adjusted in such cases by the right amount.

What should we learn from all this? Teams with injured secondaries or receiver corps are a little suspect, an injury to a kicking specialist may be important if they still play while hurt, and finally, don’t go overboard in your revision of a team’s chance just because a quarterback is doubtful!