This is the place to post questions and discussions on usage and style. The members of the Wordwizard Clubhouse will also often be able to help you to formulate that difficult letter.
Steve, there's probably too many to list. Many of the words or phrases can also be used to describe other types of victories...in an argument, in a sporting contest, in a war, etc. A common one used to describe besting someone in a physical altercation is to "beat someone up". "Kicking someone's ass (arse)" is another that you'll often hear, but that one may not be considered polite by some people. Try Googling "synonyms for winning a fight."ACCESS_POST_ACTIONS
You could say that your character had the upper hand in the fight, that he gave his opponent a beating he'll remember, that he knocked out (or even "knocked the lights out of") his opponent - if you're not a native speaker, be careful not to write "knock up" instead, that's a whole different situation - , that your character beat him fair and square, that the opponent got messed up (or f**ked up, if the context you're writing in allows it) by your character...ACCESS_POST_ACTIONS