Unfortunately people thinks only at the present, especially teenager.
Irl playing with an injured shoulder at that age = the last game of his life.
Yes, probably you will score, but is more probable that you shoulder say sayonara, and with that the promise he made to his mother.
P.S. and I don't understand why the mother leave his son. A peaceful divorce for lack of love is normal, completely fine with that, but why disappear from your son's life?