She didn't assault him. She playfully tapped him with a paper.
Sorry but the OP doesn't say that her tap with the newspaper was "playful". She said that she "pretended" to hit him and accidentally made contact. She felt it was banter but, as others have said, banter isn't necessarily always perceived as friendly or pleasant by the person on the receiving end.
Similarly, the OP's perception that the man was sarcastic in the first instance may have been wrong. He may have been being sarcastic or he may not (and the 'sarcasm' was due to the OP's misinterpretation deriving from her acknowledged dislike of him).
We don't know, The only people to witness the whole thing were the OP and the man. No, the man shouldn't have hit her but, equally, she shouldn't have 'pretended' to hit him only to make accidental contact. (What if his blow was equally "accidental"..?).
All we can say is that two adults got involved in an escalating situation. At any point during the escalation either one of them could - or should - have backed down, but failed to do so. Yes the man behaved the worst but the OP has some responsibility. Not the mostpart of the responsibility, but some : He shouldn't have hit her but she shouldn't have initiated the physical aspect of the altercation.
For those that say they can manage "banter" within the workplace (especially with people they dislike), good for them. As I explained upthread, as a man, I never banter with men (or women) that I don't know very well, it's just not worth the risk (especially if I'm alone with them, as in the case with the OP). Having worked with violent people I've learned the hard way that some people (both M&F) are on a hair trigger and you don't necessarily know what the trigger is. That's not to say I never banter, I'm just very careful who I banter with.
What does worry me about this thread is the assumption that because males in general are more likely to commit violence against women that we should then believe that all males are uncontrollably violent.
It's true that, sadly, many men are violent but does that mean they all are? If they all are it becomes an essential argument: That all men are bad by nature and can't change.
This defies both logic and any ethical standpoint. It's the same as saying all muslims are evil.
Worse, still, it allows men to argue that women have essential traits that make them inferior. Personally, I don't want to live in the lose:lose universe this represents - either as a man or a woman.