I put together the 2 clips showing Fonz actually throwing a punch and hitting someone.
s11 ep06 Glove Story (punching out a boxer in self defense for Chiachi)
s11 ep12 Like Mother Like Daughter (punching Mr.C)
s8e p21 - Mother And Child Reunion (off screen fight)
s07 Ep03 - Fonzie Meets Kat (throwing a guy over a bar)
s4ep83 Happy Days Joanie's Weird Boyfriend (kicking someone in the face)
Like everyone said, it was a family show so they did not want to show people being hit by the Fonz.
On Happy Days they NEVER or RARELY EVER showed Fonzie hitting or punching someone because it was considered to be a family show.