>>30021821A less exaggerated version of number 2. His father didn't beat him for losing, but they never got along. The dad couldn't connect, preferred physical punishment, and wouldn't accept that his anger issues were a problem (golf club explanation: he broke them when he got frustrated with Guzma's sullen, rebellious attitude. It still served to scare the shit out of Guzma, so it was hardly a "solution"). Guzma threw himself into Pokemon battling to avoid the house.
After failing the trial captain test for being a poor teacher/communicator and anger issues, Guzma was furious and swore to get strong enough that nobody would ignore his power and tried to leave on a Pokemon journey at once. His father good and loses his temper and tries to do something much harsher than he has before, but Guzma retaliates, kicks his ass, and books it.
tl;dr an It's Complicated family situation exacerbated by a stubborn father and a son afraid to show weakness. Hala's summation of Guzma postgame (that he doesn't respect his opponents and is only trying to crush them), his admiration of Lillie's rebellion against her mother, and how deeply he craves the respect of an adult (his thing with Lusamine) all point to a dude with massive parent issues who learned from an early age that violence was a good solution.
I feel like I just sperged everywhere god I wish I could sage myself. 
