I would group gambling into these 3 categories:
True gambling is playing games like roulette or craps, hoping for the best on the spin of the wheel or the roll of the dice.
Second would be sports betting and fantasy money leagues. Very skilled players will win in the long run through study, practice, etc. where they gain an edge, but utimately you leave your money up to the players on the field.
Third would be something like poker, where luck is in the fall of the cards, but you directly
affect what happens: how much to put in, what to play, etc (you make the decisions). Some days you will lose due to the fall of the cards, but a quality player wins in the long run.
So money leagues are gambling to a point, but if know what you are doing, at least you can create a cretain edge over others.