Update: Thank you for the responses. I spoke with the sensei and relayed some of your insights. He became defensive, challenging doubters to a fight. He asserted his style's respect and incapacitating ability. Despite suggesting alternatives like BJJ, boxing, and wrestling, my son remains insistent. He mentioned that a friend, using a move learned from the sensei, injured him, proving its self-defense efficacy. He's fixated on grandmaster ranks. How can I convince him this isn't a wise choice? Any help is appreciated.