The movie was made by Darren Aronofsky, who is known for making fairly disturbing movies (his movie "Black Swan" is the only movie i have rated "not for kids" so far).
You should know that this movie is not disturbing, rather talky, emotional and calm, but also has its violent moments.
The violence is very infrequent, but also very bloody and brutal:
-During a wrestling scene near the beginning, we see the wrestlers all covered in blood and gore, one of them has a large cut across his forehead.
-The second fight is very grizzly and gory: The wrestlers use staples to harm themselves and the other one. Then one of them takes a fork and violently but carefullysticks it into the other one's head (very bloody, but not that this is a wrestling movie, the scenes are not disturbing or sadistic). Then heavy objects are used to beat each other, resulting in much visible blood.
This scene is very brutal and gory, but then a long time without any violence is present.
-Then a character cuts his finger at a razor, resulting in much blood (but it is pretty much what would pass at PG-13).
-The last wrestling fight is without any blood.
Most of the movie, however, is very calm and nothing compared to other Aronofsky movies.
There is typical R-profanity.
Some scenes take place in a strip bar. Nothing explicit is shown.
A brief scene of sex, no genitalia is shown.
Right before this brief scene we briefly see the wrestler do drugs, but however, the wrestler is depicted as not very admireable and as a loser, so it is rather unlikely children will see a role model in him.
The violence in this movie is very strong, but also very VERY infrequent, most of it happens at the beginning, and after the second fight the violence gets PG-13.
It is very unlikely viewers 14 and up will have problems with the movie, and don't worry because it is an Aronofsky flick, it is a very untypical movie for him.