To be honest this is a good question. God calls us to be gentle and meek so I really have a hard time with boxing being ok with God. God calls us to preach the gospel to the lost. Boxing normally has allot of drama and hatred tied to it causing people to become rivals and enemies. To me it's contrary to the Gospel. Creating a rival and leading people to Christ are completely opposite to each other. Most people will say well i'm not trying to create rival. But obviously even if you aren't it will happen because it part of the boxing lifestyle. It's like most sports. Those players say they're Christian but once they get on the field or court everything changes. It's not suppose to be this way.
2 Timothy 2:24 24And the servant of the LORD must not strive; but be gentle unto all men, apt to teach, patient,
“And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.”
“Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves.”