CINCINNATI – Until this week, Robert Geathers’ football distinction was his family history – a father and uncle who also were NFL defensive linemen.

One hit on Kansas City quarterback Trent Green pushed him into the spotlight.

Since knocking Green unconscious in last Sunday’s season opener, the Cincinnati Bengals lineman has been put in an uncomfortable position, watching all the replays and explaining why the play turned out that way.

“I couldn’t have done anything different,” he said yesterday, choosing his words carefully and sparingly.

Game officials threw no flag on the play. Yesterday, the league office agreed, absolving Geathers. “The injury … was unfortunate and has drawn much commentary, but it is not a foul,” Ray Anderson, the NFL’s senior vice president, said in a news release.

That shoulder-down hit has become the signature moment of Geathers’ brief career.

A fourth-round draft pick from Georgia in 2004, Geathers lost his starting job this season and was relegated to rushing the passer – what he does best. He had six tackles and a pair of sacks Sunday, overshadowed by one play.

Green took off on a third-quarter scramble. Geathers was blocked from behind by receiver Eddie Kennison as he closed in on the quarterback, who went into a slide just before he was hit. Geathers’ shoulder landed high on the chest, providing the force that snapped back Green’s head.

The capacity crowd at Arrowhead Stadium booed as Green lay motionless before being taken off on a cart with a severe concussion. He’s expected to be out for a few weeks.

Chiefs president Carl Peterson fumed that the play crossed the line and should have been penalized.

“In my opinion, I think it was a late hit,” Peterson said, a day later. “I think it was obviously a very vicious hit, one that unfortunately Trent Green and the Kansas City Chiefs are paying a price for.”