The St. Louis Rams were without Robert Quinn for much of their Week 13 win over the San Francisco 49ers, thanks to the after-effects of a concussion that limited him in practice all week; he appeared in just 20 of 76 snaps for the Rams' defense, exactly long enough to get called for a questionable Roughing the Passer penalty.
The atmosphere in the NFL has reached the point where no concussion, justifiably, is considered routine. But Quinn's limited snaps on Sunday were probably by design; he'd barely practiced the week before, and the Rams would be foolish to rush their sack leader back too soon in the middle of his breakout season.
Quinn was cleared to play, and he was participating in practice by the end of last week, so it seems unlikely that this problem will persist into Week 14. But the Rams are smart to try to avoid the chance of that happening with a player on the way to 10 sacks in his sophomore season. The linemen whose playing time increased in his absence—Eugene Sims and William Hayes—each made his presence felt, so there's no particular incentive to pushing things.