When they are with their littermates and any adults, during play when they bite to hard, the one getting bite will scream at the biter… and adults will strongly correct... this is when they learn "soft" bite... so sounds like your Rocco did not get this... This happens if removed from the adults and/or other littermates too early... So as stated, all play stops... also, I suggest that if the bite is too hard, scream/yell very loud and then stop all play
