Stanford quarterback K.J. Costello will not play on Saturday against USC, coach David Shaw announced Thursday.
The senior quarterback exited just before halftime of last week's 17-7 win against Northwestern after receiving a hit to the head. Redshirt sophomore Davis Mills will start in his place.
Costello was going into a sliding motion when he absorbed a forearm to the head, but the play did not draw a targeting penalty.
"I believe the officials on the field and replay officials missed the call," Shaw said this week. "I thought it was an ejectable offense.