Colorado quarterback Sefo Liufau was sitting on the bench with an ankle injury, suffered on a big hit he received while throwing a touchdown to put the Buffs up on Michigan in the third quarter.
While on the bench, he took another hit, from a barreling Jabrill Peppers, who'd been shoved out of bounds while running back a punt. Peppers is one of the sport's best athletes, and a couple trainers arranged very near to the sideline is probably not gonna stop him, and there's not a whole lot he could've done to avoid plowing into that humanity.
The total panic on the faces of everyone around him is completely understandable.
Another view, via BTN:
Liufau went back onto the field on CU's next drive, despite the ankle injury and the speeding helmet right to his naked face, but after another big hit, he limped into the locker room.