I think there's a difference between jostling/pushing the unofficial away as opposed to intentionally cloberring of the unofficial - I dont think you have the right to intentionally clobber anyone. Besides, if you are the official, and a fight starts - you are always at the losing end - in a fight, you lose your time to get the shots you need, you may end up at the police station for causing hurt, and the client may not take too kindly on you intentionally clobbering anyone, whether or not you were entitled to. Push and jostle all you want, but do not intentionally clobber anyone.
Violence is never the answer, I hope the other new professionals don't get the idea from your post that it is all right to do so.
And by the way, I've been on both sides of the fence before, so I take a balanced view. If I'm the official, just say nicely or at most, if stubborn, push him away. If I'm the unofficial and you intentionally clobber me, be sure that you'll on your way to the police station and miss the event that you're paid to cover.