"Slip him a buck"

This is from an article about how to raise a good kid: Your son is getting aggressive on the basketball court. The referees never see his well-placed elbow or the sly trip. Do you remind him that good sportsmanship is as important as winning? Or do you slip him a buck for every basket he makes?

Question:(buck might be a dollar, I guess, so giving money every points his son achieves?)

ANSWER: Yes, you are right, a buck means one dollar. Slip him a buck means to pass quietly or secretly without attracting notice. The slang phrase means to give or pay on the sly. Thus, someone is asking the father,"Do you give your son money for every basket he makes?" A buck means a dollar, but this phrase could also mean to secretly give more money than that, e.g., he could have given him five bucks for every point he made. (That could be five one-dollar bills or one five-dollar bill.) So, if your mother slips you a buck, she gives you an unspecified amount of money without your father knowing about it. I hope this helps. "Ambiguous Bill"