Were you there, if not then you need to fall back. Anybody who's been in a relationship should know that it's almost impossible to judge from the outside looking in. I'm not defending Mayweather beating his girl/wife or whatever, I'm just pointing out that unless you were there then you don't know exactly what happened.
Did she have a gun? Nope.
Did she have a knife? Nope.
Was his life threatened at any point? Nope.
Were the kids threatened by her? Nope.
He dodges punches for a living. There ain't no way she's gonna hit him with anything outside of a bullet. I understand folks get heated in arguments. That happens all the fukking time, but only way I'll say it was justified is if he or his kids felt threatened and if that happened I guarantee you he wouldn't be in jail. She would be.