With all the wrestling/boxing allegories in this thread, I decided to do a special Bonus Round of three episodes that actually has boxing/fighting in it!
DS9 - For The Uniform (S5)
VOY - The Fight (S5)
B5 - TKO (S1)
Does Tsunkatse count? That's probably better than the three episodes above and it's based around fighting. Plus it's got The Rock, Jeffrey Combs & J.G. Hertzler in it.