Sounds to me like LaBeouf, an inexperienced stage actor, was trying to give an opening night performance on the first day of rehearsals.
People I know who have worked with Sullivan claim he's a very hands-off director in terms of directing actors (i.e. he gently nudges talent in the right direction rather than digging in and micromanaging their work).
LaBeouf needed a micromanager to get him back to basics, Sullivan wasn't it, Baldwin knew it, and had him fired.
Just my theory.
"Impossible is just a big word thrown around by small men who find it easier to live in the world they've been given than to explore the power they have to change it. Impossible is not a fact. It's an opinion. Impossible is not a declaration. It's a dare. Impossible is potential. Impossible is temporary. Impossible is nothing.”
~ Muhammad Ali