New York ? The NFL absolved Cincinnati defensive end Robert Geathers on Wednesday for his hit on Kansas City quarterback Trent Green, emphasizing quarterbacks are responsible for avoiding hits by sliding.

Green sustained a serious concussion last Sunday after a hit by Geathers and will miss at least two or three games.

“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 statement.

Anderson said a review of the play in Kansas City showed Green started “a late slide” as Geathers prepared to tackle him. At the same time, Geathers was blocked in the back by a Chiefs player, was no longer in control of his body and twisted to avoid driving his helmet into Green or hitting him helmet-to-helmet.

Geathers’ right shoulder, however, hit Green’s shoulder and drove Green’s head into the ground.

In a memo sent to all 32 teams Anderson said: “On sliding quarterback plays, the responsibility of defenders is to avoid a sliding quarterback while the responsibility of the quarterback is to use the protection properly. This rule will continue to be strictly enforced, and violations are likely to result in disciplinary action.”

Anderson said quarterbacks who want to take advantage of the protection of a slide must start it before the prospect of imminent contact.

He cited a play in the Seattle-Detroit game as an example of an illegal hit. In that case, Seahawks quarterback Matt Hasselbeck broke out of the pocket and began a slide. Lions rookie linebacker Ernie Sims, who had the opportunity to avoid contact, drove his helmet into Hasselbeck while another defender, Cory Redding, jumped over the quarterback.

Sims drew a 15-yard penalty for unnecessary roughness. Anderson said the play was being reviewed for a possible fine.