I agree with most in here that physical fights are exceedingly rare in rec tennis. Most the time, the confrontations are passive aggressive, with people saying snarky things to each other, acting rude, or just hooking on line calls where they can. However, I have seen a couple incidents that got physical.
I won't name any names to protect the innocent, but we had two teammates get into it after a practice last year. Both guys super nice, so it was really weird to witness, and it turned out the whole thing was started over a misunderstanding. Player A was having a bad day, and muttering under his breath about how badly he sucked. Player B thought that Player A's comments were actually directed towards him, and was secretly steaming inside. Player B wins a close practice set, and in frustration, Player A hits a ball hard over the fence and out of the court, but it hits a suspended walkway behind the courts and bounces back. Player B had his back turned and didn't see what happened, but the rocketed ball bounced near him, and he believes Player A intentionally hit a ball at him after the set was over. Player B, who is a former Mr Olympia level body builder and in incredible shape, loses his mind, charges Player A, and starts screaming obscenities while pushing Player A's face and chest. Player A, who is about 6'3 and 230 lbs, is shocked and wisely refuses to engage physically. Player B then storms over to the bench, throws his racquet bag, and proceeds to punch the 10 gallon Gatorade jug between the benches so hard, it flies about 15 feet and splashes down in the doubles alley of the adjacent court. He then huffed off... screaming... with a broken hand. This was just a few days before Nationals, and his tirade cost us his services as one of our better players at the event... but it also meant I got to play one more Nationals match than I expected... so...
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Another time, over 10 years ago, my doubles partner got into a shoving match in a USTA league match with one of our opponents. Opponent thought we made a bad line call on a serve. His partner disagreed as we all saw the ball land about a foot out. It really wasn't a close call, very routine, and three of us all saw it that way, and there hadn't been any disagreements before this. However, opponent won't let it go and keeps cussing at us and calling us cheaters. I'm getting pissed, and I'm returning the next serve, so I decide that if I get a forehand, I'm going to hit my shot up the line as hard as I can right at him... which happens, and it nails him in the chest. Opponent throws down his racquet and charges over the net at me. I stand my ground and opponent is screaming and pointing his finger in my face. My doubles partner (who is about 6 inches taller than both of us, former military, and a former hockey player) jumps in and starts pushing the opponent back. Opponent starts pushing my partner, saying he's going to kill us both. Players from opponent's team come running off of other courts and pull him away, taking him out to his car. Match is over at that point. Opponent's doubles partner and their team captain are flabbergasted and apologizing profusely. Opponent's captain encourages us to file a grievance against his own player, which we do, and he gets banned for the rest of the season. Fast forward a decade, I'm now (cautious) friends with that opponent, who is always exceedingly nice whenever we play, and I am a member of that captain's team frequently... so I guess it had a happy resolution?