A cliché among sports fans is that injuries are not an excuse for losing, but in truth, injuries are in fact a very good excuse. In fact, having your good players unavailable and replacing them with worse players makes a team noticeably worse, and almost nothing correlates better with winning than injury rate.
Of course, not all injuries are created equally. If your backup running back is injured, it really doesn’t matter. If your starting quarterback is hurt, it matters a great deal. Every year, Football Outsiders publishes Adjusted Games Lost (AGL), which attempts to account both for the quality of injured players as well as for players who may be playing while hurt.