Obviously, because of the way injuries clustered this season, there's no way to isolate the effect the loss of Joe Addai has had on the Indy offense. Losing Collie and Clark at the same time made for quite the divot in the Colts offense.
However, one thing Indy has replaced is Addai's production out of the backfield catching passes. Addai was fourth on the team with 51 catches in 2009, and he was on pace for 48 more this year. Obviously, losing 30 catches in half a season is a lot for an offense.
Fortunately, Don Brown has been around to do the heavy lifting.
Through six games, Indy RBs caught 21 passes (18 Addai, 2 Brown, 1 Hart) for a total of 149 yards and no scores. That's about 3.5 catches a game for 25 yards.
Over the last 8 games, Indy RBs have caught 33 passes (18 Brown, 9 James, 3 Hart, 1 Rhodes) for 266 yards and still no scores. That's 4.1 a game and 33.3 yards a game. Indy is averaging a yard per catch more over the last 8 games.
Most of that increase in yardage has come from Don "Everyone Hates Me Unless I Do Something Good" Brown. Brown has been dynamic out of the backfield this year, averaging 10.3 yards a catch. That's the highest YPC for a Colts back with at least 15 catches since Marshall Faulk in 1998.
Don Brown may have had a disappointing start to the year, but he has been amazing as a pass catcher. For those who like advanced metrics, the Outsiders have him at a 33.1% DVOA (8th in the league) as a receiver. In comparison, Joe was at -0.4% (basically league average).