
One of my girls is ball obsessed I use it to my advantage as in that she has her own balls which she gets only when we go to the park it then gets popped back in a bag when we have finished.
I take with me 2 small balls and 1 large ball but I have also taught her to hold onto a rubber bone while we play the game!! she then doesnt grap the ball with her teeth she actually stops it with her legs then waits for it to be kicked again. what I find amusing is the way she spits out her bone when the game is over ..LOL
We went through the stages of pinching peoples balls in the park and this is how we solved it , if she spots a ball we just shout 'where's your ball' and bounce it once and she focus' on that while we get past the other person.
My son plays football in the garden with my dogs maybe if you son had a game with Jack then put the dog inside while he played alone . Also teach him to hold a toy while he plays would help, Jack is young enough to change his habit if you let him do it he will continue.
HTH
Roni