Whose fault is it? That's what I asked when I wrote about Indianapolis Colts running back Trent Richardson on Tuesday afternoon.

RichardsonRichardson, the play calling or the offensive line?

Lee Singer from ESPN Stats & Information was nice enough to crunch the numbers. Here's what he came up with:

ANGLE #1 – Does Richardson not have room to run?

Quote: Coach Chuck Pagano said Richardson has been, for the most part, a victim of circumstance, suggesting there hasn't often been room to run. "You look at Trent's runs, for whatever reason, there's penetration [by defenders]," Pagano said. "You feel bad. A guy gets the ball handed off to him and all of a sudden, there's a guy sitting there for whatever reason."

Support: There’s some truth to this. Richardson has been first contacted in the backfield on 19 percent of his rushes; the rest of the Colts' running backs have been hit in the backfield on 13 percent of their rushes during that time. Among the 34 NFL running backs with at least 75 rushes since Week 3, Richardson’s percentage is ninth-highest.

Richardson is averaging only 1.5 yards before contact with the Colts. Only three NFL running backs have a lower mark since he joined the team. Donald Brown, on the other hand, has averaged 3.7 yards before contact, which would lead all running backs if he qualified.

Argument against: Excluding rushes where he was hit in the backfield, Richardson is still averaging only 3.6 yards per rush with the Colts (league average 5.0). When he has been hit, he’s averaging 1.4 yards after contact per rush (Brown 2.4).

ANGLE #2 – Are defenses selling out to stop the run?

Quote: Richardson suggested to the Indianapolis Star that opponents have sold out against the run, particularly on early downs. "If I don't have big runs because they're trying to stop the run, then I feel like I'm doing my job," he said.

Colts RBs vs. 8+ Defenders in Box Richardson Brown Pct of rushes 16% 19% Yds per rush 2.1 5.9 Negative rushes 5 1 Source: ESPN Stats & InformationSupport: The Colts have a 50-50 play-calling split on first down with Richardson in the game but a 68-32 pass-run split with Brown in the game. That would make the Colts the league's pass-heaviest team on first down. Richardson is averaging 2.8 yards per rush on first down, while Brown is averaging 4.3. Overall, the Colts have a 64-36 pass-run split with Richardson in the game and a 69-31 split when Brown is in.

Argument against: Brown has actually seen a higher percentage of eight-plus defenders in the box on his rushes than Richardson and has had more success in that situation.