He plays all year because Grimes doesn't care what CB thinks and he doesn't get hurt.
If he does get hurt it will be in the first half of the year, like against Wisconsin or Washington. Grimes looks at the QB's on the bench and decides he doesn't want to see his potential Freshman phenomenon carted off the field on a Gator or so demoralized by the whooping he is about to take that it takes forever to bring his confidence back. So Grimes goes with Critchlow. He is nothing nearly as special as Lamb believes but a serviceable QB. BYU goes bowling but loses the bowl game.
2020 a real battle for QB ensues.