We've all heard that the Steelers are complaining about the Ravens chop blocking during the game Sunday, particularly Casey Hampton accusing Marshal Yanda. So I did a little Google search on chop blocking and found this at ProFootballTalk

But the Steelers, and folks like ESPN’s Merril Hoge, apparently don’t understand the chop block rule. An illegal chop block doesn’t occur when, for example, the center engages the nose tackle and one or both of the guards block him low. Instead, an illegal chop block happens only when the offensive lineman delivering the low block was originally lined up more than one position away from the offensive lineman who initially has engaged the defender. Here’s the official rule, which a league source has forwarded to PFT: "On a running play, A1, an offensive lineman, chops a defensive player after the defensive player has been engaged by A2 (high or low), and the initial alignment of A2 is more than one position away from A1. The rule applies only when the block occurs at a time when the flow of the play is clearly away from A1." And so, if the center hits a guy high and a tackle hits him low, it’s a penalty. When it’s a center and one of the two guards, the chop block is not illegal.

Since Hampton was engaged by Birk at Center, and Yanda is one position away at RG, it is not an illegal chop block. Or maybe Hampton thought Yanda was still playing RT. In any event, what Hampton should be worried about is getting pancaked by Birk on Rice's TD run.