Consider I run a rock paper scissors matches online, where users buy in and cash out money if they win. Would this be legal in the United States? It is somewhat similar to esports tournaments, where teams buy in to participate in a tournament for a cash reward. Although many consider rock paper scissors luck, there is virtually no "chance" involved, and there are ways to predict an opponents move based on their previous match history.
This activity would be very likely to be considered gambling under U.S. law, because the person making the bet has to assess the probability of something outside his control happening and bet accordingly.
The fact that some people are better than others (particularly with access to information from past contests) at judging the probabilities at stake does not mean that something is not a "game of chance". Any situation that calls for a participant to predict probabilities is a "game of chance" as opposed to a pure "game of skill" even if skill at predicting probabilities materially improves your chances of success (e.g. blackjack is still a game of chance even if the casino permits you to engage in card counting).
Similarly, while sports betting requires skill, it is still gambling when you aren't personally playing the game, since the skill involved is an ability to predict the probabilities of an outcome and not the skill involved in playing the game itself.
Furthermore, it is not a probability based decision in which there is either an insurable interest in the outcome (because the outcome results in injury to someone or something in which a participant has an intrinsic economic interest apart from the bet), or in which the bet is an action which has economic reality apart from the bet (as in the case of a stock market or commodities market investment).
The legal implications of the fact that this is very likely a form of gambling is not alone enough to determine the legal consequences of that fact, which are beyond the scope of this post. Many other law stack exchange posts have grappled with the legality of Internet based gambling, in general.