To hit a child round the head so hard they would see stars/be dizzy/have a headache?
My stepfather did this often, and I know standards have changed (I am vehemently against ALL smacking and have clashed on MN over it before) but when it's your own memories it can be hard to judge what is and isn't, iyswim
The whacking around the head was not the only thing that happened, some of it I know was wrong/illegal, other bits I'm not sure.