Dear Orthonormal, You are partially correct. it may be true that the way I use game of skill/luck it is not the ususal one, but it is a reasonable way, more solid, in my opinion, from the point of view of game theory/economics, and more importantly, it is relevant to the usage in the relevant laws which was meant to define what gambling is, and to common wisdon regarding gambling

The conventional way does not give you a way to measure the ingredients of skill and luck, and it treats the bare game without taking into account the entire scenario, the game, the betting, the winners, the enterance fees, etc

When you try to determine what is a gambling activity and what is not, looking just at the bare game is insufficient the common wisdom regarding these 50 years old poker clubs in J-m is that what was going on there was a gambling activity Aumann proposed a loophole in the legal definition of gambling based on luck and skill ingredients However, if you examine the situation carefully you realize that the usual meaning about what is game of luck/skill is insufficient, and is not compatible with the usual meaning of what is a gambling activity. A more careful analysis based on the entire scenario is more appropriate

In any case, the difference is not between tennis and poker, and it is not based on ethical boundaries (I do not have strong opinions about whether gambling should be legal). The difference is between high stakes negative- expected-rewards games and high stakes games where players expect positive rewards