I haven't been able to make a precise count, but 4 teams either stayed in their lockerroom or sat/knelt en masse during pregame ceremonies. That's the equivalent of 184 active players, or 14.3% of active NFL players in today's games. 25% would equal 325 active players in today's game and Monday night's. I'm guessing that nearly every other team had a couple players sit or kneel, but probably not enough to get the over.
