I just found an article from last June about him...
Bryce Harper is going to get himself hurt
Check out the home run that Nats prospect Bryce Harper hit last night. Specifically, check out the way he stopped to admire it and the kiss he blew to the pitcher when he crossed home plate:
Yes, hes young. But theres no excuse for that kind of thing. Even someone who cares as little about the unwritten rules as I do has to appreciate that Harper is being disrespectful here. That pitcher is trying to do his job. He didnt get $16 million to tide him over as he tries to get through the minors like Harper is.
Maybe he gets away with that kind of thing in A-ball. But if he doesnt learn a bit of humility at some point on his journey to greatness, hes going to get his ribs broken.
So, yeah, looks like he probably does have a little too much cockiness in him for a rookie.