My brother has a traumatic brain injury from a car accident and he has no impulse control and no control over his emotions.
"Fortunately" for him, he's so fucked up he can't live independently or drive or do anything basically so he has to be taken care of by my mother and I.
These boxers probably have lost their impulse and emotional control but since they aren't bound to a wheelchair and are independent adults, they can get into a lot of trouble. My mom and I have had nightmares of my brother getting into trouble.
I don't recall Jermain being a trouble maker or ex-thug but what we do know is that on top of the regular damage a boxer takes throughout a career, he also got brutally KOed by Arthur Abraham which probably changed his brain forever.