This is not a bad movie.
Ok let's look at the bad facts
It's been done before. It's like 8 mile meets rocky.
The choreography is appallingly slow and unrealistic and far too 'flashy' at times (groundwork & rolling for example). It's predictable, from sleeping with her trainer, her abused past and the inevitable outcome
That's it really.
Other than that, Halle Berry's portrayal is first class (as ever) and the acting from the young man is superb! (and he only says three words in the entire film) and for all those starting Berry doesn't look the part? She was in as good a shape as 'ladykiller' and probably 20 years older.
Halle rocks and her fitness is impressive. And there's nothing wrong with the directing at all. It attempts to portray a lot of the world through the eyes of the child, without actually doing that. And it works.