I gotta be honest most of the fights in the film aren't very vicious or hard hitting. So its the most unoriginal overused plot formula you could possibly decide on. This ring is run by a mega rich Keanu Reeves and his entourage who sets these fights up for other mega rich people to enjoy, oh and the cops are after them too. The reason he was chosen is because he is a skilled fighter in the art of Tai Chi which is unusual.
He needs this dosh to help save his Masters temple which is in ruin. Yes that's your plot right there, a simple humble man is lured into an illegal underground fighting ring with the promise of getting paid lots of dosh. Presumably the story is similar to his actual life in the sense of trying to show or promote how Tai Chi can be a martial art, not that he entered an illegal underground fight to the death circuit.
This film is based loosely on the real life events of the main lead Tiger Chen (yep that's his real name). The first film of 2013 set in the Far East starring Keanu Reeves, his second Asian film came out a month later (in the US).
