I have a question about pitching?

Hi, my friend is 15 going on 16 and he's one of my good friends....he's starting pitcher for varsity baseball at my school and his team is really good they played alot of games and only 1 game by 1...anyway he's a pitcher and he always throws curve he said he doesn't have arm pain but I don't want anything bad to happen he has games like 2 or 3 times aweek and practice everyday he sometimes plays shortstop but not usually...but could this hurt his arm??? what could happen if he keeps doing throwing???