In the film shooting scene in Hail Caesar (2016) the actor enters and the director meets him:
here the scene starts:
Before any scene the actor reads the dialogue and peforms it. But here the actor directly acts for the shot. How come?
Because Hobie Doyle was totally unprepared for the shoot.
You have to remember two things:
In short, Hobie Doyle had no time to prepare for this film, and his lack of knowledge of the type of movie he is now starring in may have meant that even if he did have the time, he wouldn't have been all that prepared.