Witnessed yesterday on the beach. Young (teen?)boy building sandcastle with Dad. Goes over to girl (presumably sister) who is lounging in inflatable in sea and pours a bucket of water over her head. She is upset, he does it again, she is crying. Dad sees and shouts him back telling him off. Boy shouts angrily and then tries to swing for girl (dad separates) and then swears at and punches Dad.
Dad walks away with girl comforting her.
Big scene on beach, what would you do as the parent?