Given the sequence of events it seems highly improbable that it was a setup...
Breitbart had revolt in their ranks because they turned their backs on their reporter and tried to hush the story up... Breitbart was slavishly fawning over Trump previous to the event...
The reporter in question quit due to their failure to back her up, as did one of their editors and their spokesman...
There is the video that the police felt was evidence of assault, witnesses, and also an audio tape that was recorded of the entire event.
The guy has a well known history of this sort of behavior...