The 1980s sounds like a really bad time to be a men's tennis fan. The country club sentiments of players like Rod Laver and Bjorn Borg was long gone, and the single-minded game focus of Pete Sampras and Roger Federer weren't around yet. The two dominant American players of the decade, John McEnroe and Jimmy Connors were both me-first jerks who would do anything to get ahead -- perfect microcosms of everything that was wrong with the 1980s. It would be as if your only choice was rooting for the Patriots in the NFL today.
As for the movie, it's about Jimmy Connors being a jerk. And being a jerk in such a way that he made the fans like him anyway. This is apparently a very important tennis match for tennis history, but as a person with only a passing interest in tennis, it was unfamiliar to me. I think hardcore tennis fans will get more from this movie than I would.