MLB's Lance Lynn Ejected After Hurling Belt At Umpire

White Sox ace Lance Lynn was thrown out of a game Wednesday night ... after he hurled his belt at an umpire during a foreign substance check.

The bizarre scene all went down after the fourth inning of Chicago's tilt with the Oakland A's, when third-base ump Nic Lentz attempted to check Lynn's gear for sticky stuff.

Lynn, clearly upset that Lentz didn't make a quicker effort to get to him before he got to the dugout, left his hat and his glove at the steps for Lentz to check.

When Lentz asked to see Lynn's belt too ... that's when the 34-year-old pitcher took it off and straight-up tossed it at the guy.

Immediately, Lynn was ejected ... and both the right-hander and Sox manager Tony La Russa came out of the dugout to argue.

Alas, Lynn's ejection was upheld ... and after the game, he was NOT a happy man over it all.

"[Lentz] was late getting over," Lynn said, "so I left my glove and my hat, and then while I was going down in the dugout, trying to see the trainers because I'm dealing with something, he yells at me that he needs to see my belt."

"So I toss it up and then he throws me out."

Lynn continued, "Obviously, I hurt his feelings ... he threw me out because I tossed my belt, and I said, 'Well, if you were on time, we wouldn't have this problem.'"

For his part, La Russa didn't necessarily disagree with the call ... saying players shouldn't be throwing equipment at umps.