Trespass to the Person question please help?

What does the law say if late at night in a bar for example someone called Barry, Michelle‟s former boyfriend named Alan comes up to their table and starts to chat to Michelle.

Drunk Alan told Barry to “clear off and leave Michelle alone if [he] knows what‟s good for [him].” Barry then puts his hand on Alan‟s shoulder, telling him “don‟t be like that, Michelle and I are only mates now even though she still fancies
me.” Alan punches Barry in the face and he falls to the floor. Alan then wanted to kick Barry in the stomach but was stopped by Michelle who is pushed away by Alan and falls against the bar badly cutting her head.


And what cases would you recommend me to have a look at in order to gain more understanding about this issues.
thank you