How can i get my little bratty brother to leave me alone????

every time my little brother comes to my grandparents' house to either spend the day or spend the nigh, he always bugs me. he punches me in the nose, slaps me in the face, says he hates me, always blames me for his bull crap, tries to push off a trampoline. and ever time either our mom or our grandparents' find out what he does they talk to him like he is a baby?