I have four boys and each one of them played all 4 codes of football. I never saw any really bad behaviour in junior rugby, soccer or AFL but I did see it in junior RL in the Parramatta district.
In that last game I spoke about my son's team who were running well outside the top 4 played the undefeated top side. We scored about four tries in the first half and held the other team scoreless. The other team had 3 or 4 players sin-binned for out-an-out violence and the penalty count was about 10 - 1 our way. As the ref and touch judges left the field at half-time they were approached by the other team's coach and one other bloke. They were jostled and hassled all the way off the field. I left in disgust.
Apparently in the second half, the violence was still bad but not quite as bad as the first half and the penalty count was reversed. The other team scored 6 or 7 tries, held us scoreless and won easily.
I wrote a letter of complaint to the Parramatta district JRL but never got a reply.