All hell broke loose when Dillon Brooks hit Donovan Mitchell below the belt during the Cavs vs. Grizzlies game on Thursday ... with both players getting ejected after a physical altercation.

The heated moment went down in the third quarter of Cleveland's 128-113 win over Memphis at Rocket Mortgage FieldHouse ... with Brooks missing a shot and throwing his arm back -- making contact with Mitchell's groin -- as he fell to the court.

Mitchell -- who's been dealing with a groin injury this season -- immediately retaliated by throwing the ball at Brooks and shoving him.

Players and coaches for both teams intervened before things could escalate even worse ... but both players were booted from the contest.

Mitchell went after Brooks in his postgame presser ... saying the guy has a reputation for being a dirty player.

"That's just who he is,'' Mitchell told reporters. "We've seen it a bunch in this league with him. Him and I have had our personal battles for years."

"Quite frankly, I've been busting his ass for years."

"This has happened to other players throughout this league, and it's bulls*** if I'm being honest with you," he added. "It's complete bulls***. It's one thing, you know, you got Ja [Morant], you got [Desmond] Bane, you got Jaren Jackson. Those guys, they talk s*** and that's fine, that's all a part of basketball. We all grew up playing that way."

"But when you start doing little cheap s***, that ain't it."

Cavs coach J.B. Bickerstaff also addressed the scuffle ... saying, "A guy should have the right to stand up for himself. I thought Donovan did that. I'm proud of our guys."

"We don't have those guys that start s***, but we have guys who don't run from s*** and you have to in this league."

Mitchell says he will appeal the ejection -- as he says he was defending himself.

The Cavs backed Mitchell in the locker room after the game ... honoring him with the Junkyard Dog Chain, which goes to the grittiest player of the game.