Casey Hampton, reputed target. (Bob Leverone / AP)

The NFL offered clarity on the rule concerning illegal blocks:

The rule, as sent to Pro Football Talk:

“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.”

Which means, as PFT says, 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.

Filed at 3 p.m.

The Pittsburgh Steelers say Casey Hampton was a marked man last week in their season-opening loss to the Ravens in Baltimore.

Hampton, they say, was the target of cut blocks — some of which were illegal — by Ravens right guard Marshal Yand

“You can get hurt from an illegal chop block, but I guess it isn't an illegal chop block if they don't call it,” Hampton told the Pittsburgh Tribune-Review.

No penalties were called on the blocks. (The Tribune-Review reminds: A cut block is a block below the waist when a player is not engaged with another player. It is illegal to cut from behind. A chop block occurs when a player is engaged with another player and is hit below the waist.)

Baltimore rushed for 170 yards on the Pittsburgh defense and Hampton wasn’t alone in his frustration.

Safety Ryan Clark: “It is dangerous. Until offensive players start getting hit low — because we can't hit them high — and some of those guys go out, an equivalent can't be drawn.”

Photos from The Steel Curtain

Nose tackle Chris Hoke: “Some of the things they were doing were questionable rules wise and dangerous.”

Defensive end Aaron Smith: “They made rules to protect guys from so-called chop blocks. I don't know if it is hard for the referees to see that stuff because there are multiple people falling on the ground to determine what happened.”

Hampton said he was cut or chopped on Baltimore’s first four running plays. On the first play, on which Ray Rice ran 36 yards, Hampton contends he was chop blocked by Yanda.

“There is really nothing you can do when you are engaged and fighting with a guy and they come chopping at your legs,” Hampton said. “If it keeps happening, something is going to have to happen. I can't keep getting chopped up like that when I am engaged.”