Kansas City Chiefs quarterback Matt Cassel left 9-6 loss against the Baltimore Ravens with a head injury.
In the latter half of the fourth quarter, Cassel was hit by two Baltimore players on a pass play and laid on the ground for several minutes.
He eventually walked to the sideline and went into the locker room. Brady Quinn took over under center for the Chiefs.
Cassel had been having a tough day as he was picked off twice and also lost a fumble. He was 9-for-15 with 92 yards and also had 14 yards on four carries.
On the season, he has been picked off nine times and has also lost four fumbles, while passing for just five scores and running one in.