I really liked this movie, on the whole: it was intense, well acted, had some real fun cinematography, but on the whole I found the characters profoundly unlikable, which I think was the point, but that kind of made the last scene excruciating, since a) I really had to pee by then and b) I didn't really much care by then whether or not Art got his shit together and realized that all of his relationships are based on tennis so he should just give in and strive for this facsimile of his wife's love. Or maybe just try and fix Pat? I mean I dunno maybe this year is the year for a 31 year old smoker to win Wimbledon or whatever.
Comparing this to the other main contender in media-about-how-tennis-people-are-fucking-batshit-looney, Infinite Jest, there is an interesting parallel between Tashi and 'the Moms' and the Freudian psycho-sexual, apparent, nature of Tennis (I only played for College PE credit and I must have missed that day). Both are presented as domineering figures who are both responsible for training tennis athletes, but do not play tennis themselves. They both foster hyper-competitive environments and reward excellence in tennis with sex.
In Infinite Jest Eschaton is a simulacrum of nuclear war that only the younger students play. They are allowed to do so by the overbearing academy administration, headed by The Moms and her brother, because the game involves tennis balls, trigonometry and aggression, all things which academy is trying to teach. This game ultimately devolves into actual violence one day because one of the players deciding to aim at the player instead of the game board (see this recreation by the Decemberists, and to be fair, Ann Kittenplan was fucking obnoxious). Challengers, conversely, has Tashi risk nuking her marriage over her seemingly pathological need to see good tennis. (Oh and also her family situation, as they seemingly added for only extra stakes and to indicate that her child's well-being was also secondary to tennis.) But she does this for ostensibly the same reason: to cheat at a hyper-competitive game. While Infinite Jest is somewhat more grand and absurd in scope: the psychotic tennis people are operating at the academy level and the fact that some of them are related only serves to underscore the alienation of all of them, Challengers is much more intimately confined to power dynamics of the thruple.
And given all of that, I kind of wished Art had found some third way out of the weird power struggle with his wife. He's clearly hurt by her meddling/infidelity which allows Pat to even the score as Art stops returning serves after the revelation that Pat had slept with his wife (like the other day, not in the flashback.... I mean also in the flashback, but Art's not mad about that because that's before he snaked Tashi away from Pat). So, anyhow, it ends with Art giving a shit and (I think) scoring a point. I don't know if you're allowed to touch the net like that or if he reached over the line is that all kosher? In my head cannon he wins and leaves Tashi for Pat, who is also a self-proclaimed shitty person... fuck... honestly I hated them all by the end and kind of hope they murder/suicide eachother. Don't worry: the kid has a grandma who is already basically her primary caregiver.