Rogue, if you haven't read it yet the second volume of Farel Dalrymple's Pop Gun War has a plot strand involving a part-cyborg character getting caught up in an alien boxing competition - there's some neat ideas there that might help jog your creativity.
Failing that, you could always have some sort of additional element which introduces a non-boxing option for the TKO (like chessboxing, but maybe weirder or more exhilarating than chess).
As far as an introduction to boxing goes, you could do a lot worse than the recent Jawbone. It's not a documentary but Barry Mcguigan trained the lead actors for the boxing scenes and it spends a lot of time showing how boxers train and prepare for a fight.