Watch that video several times. I will tell you what I see.
Acosta gestures with his left hand towards the President, pointing his index figure at the President as a "one" as he is asking for one more question.
The White House intern approaches from Acosta's left and tries to get the microphone and Acosta will not surrender it. She is blocked by his outstretched left arm and instead of going around him, she reaches under his outstretched left arm and attempts to pull the microphone down and away from him.
This action pulls Acosta forward and his outstretched left arm goes down. He quickly pulls it back and says "pardon me, ma'am."
I realize I'm in the minority on the right here and there is a lot of loathing on the right for Acosta. I get it. I just disagree that this was intentional. It looks very accidental to me. I'm sure your mileage will vary.
Regardless, this is a silly story. Jim Acosta should apologize, say it really was an accident, and say he didn't intend to push her away like that. The White House should let him back in. We've got more important things to focus on, like the GOP being able to expand the number of conservative judicial picks.