Sproles caught a pass from Philip Rivers and had turned to run when he was hit by McClain. The Raiders linebacker led with his shoulder, but the side of his helmet hit Sproles' helmet. Sproles was on the ground for a few minutes before walking off the field.
The hit was legal, referee John Parry said after the Raiders' 28-13 win.
"We had three guys looking at it, the back judge, field judge, line judge," Parry said. "All three felt that he gained possession, took a minimum of three steps and now he is considered a runner so helmet-to-helmet contact is off.
"You can't hit helmet-to-helmet on a defenseless player," Parry added. "He was not considered defenseless. He was considered a runner because of the act of possession was complete, the minimum of three steps were taken, so he was now deemed to be a runner so helmet-to-helmet contact is legal."
Sproles didn't return.