...announcements.
If a guy has told the staff that he wants to RS, then he just won't play v PSU.
It's still a FB game, so Ucla's coaches won't want to tell PSU who won't be playing. Make PSU waste time preparing for everything...it might pay off with a play here or there during the game.
And sometimes RS plans change. Say, the starter gets hurt. Or plays really poorly. Or both. The kid might decide that, based on the other work I put on film, and now the new opportunity to put more plays on film, it is a sound business decision to play out the season and try to do the best I can.
I'd say, if a kid you expect to be on the field is conspicuously absent (even if he's suited up), it might not be a coach's decision or an injury. It might be an implicit decision by the kid to preserve a year of eligibility.