may film was given a 12a certificate due to:

• Misuse of drugs must be infrequent and should not be glamorised or give instructional detail.-when billy takes drugs to cope with his loss
• Sexual activity may be briefly and discreetly portrayed. Moderate sex references are permitted, but frequent crude references are unlikely to be acceptable-when billy and Maureen have sex after the first fight
•  There may be moderate physical and psychological threat and horror sequences. Although some scenes may be disturbing, the overall tone should not be. Horror sequences should not be frequent or sustained.-When billy goes to find Hector in his house.
• There may be moderate violence but it should not dwell on detail. There should be no emphasis on injuries or blood, but occasional gory moments may be permitted if justified by the context. Sexual violence may only be implied or briefly and discreetly indicated, and its depiction must be justified by context.- I could disagree with this as the commentators at the fights with billy did draw attention to the cut above his eye.

in my film Southpaw has in my opinion a lot of violence for a 12/12A I think this because the BBFC has said that there may be moderate violence but not be dwelled on detail