Didn't we all pretty much know Rex was going to start this game as soon as Doc said he had big news?
Maybe the players were sort of taken a back, but let's not act like they go in the huddle and all the sudden they saw Rex and they were like "WHOA, DUDE, IT'S YOU THIS WEEK!?". Rex and Beck split reps during practice all week, and all the players would've known who was the starter well before the game started. It's kinda nutty that Mike didn't let everyone know sooner, but it's not that big a deal. Not sure knowing which quarterback would've changed the outcome, and the offense took a minimal step forward despite it. Didn't seem like the players were deeply affected by the shift from a godawful quarterback to a mediocre one.