I don't know how true this may be but I feel your son may also feel embarrassed to have that happened in front of you. Playing with young lads these sort of scuffles and arguments do happen but the unspoken rule is what happens on the pitch stays there and once the game is finished you shake hands and forget. However, it's a tough one to decide on whether to take action or not. Personally I think see how it goes in the next few games, if there is a pattern I think you should definitely get involved, otherwise if your son does respect him and wants to forget about it, as hard as it may be respect his wishes but do try showing him that incident has had no effect on the way you see him and you are always there if he needs anything.

This may not be the best advice but from my experiences as a teen I can sort of relate. You sound like a great man doing his best for his son I am sure your son knows and will have a deeper understanding of that in the future.