Mavericks Fan Ejected From Game After 'Fire Nico' Stunt

A Dallas Mavericks fan was booted from the team's home matchup against the Sacramento Kings on Monday ... 'cause apparently calling for the GM to be fired for trading away Luka Doncic is a big no-no.

It all went down at the American Airlines Center, where at least two Dallas supporters made their frustrations with Nico Harrison crystal clear.

They had two bright poster boards that read "Fire Nico" on them ... but if that wasn't enough, one of the guys also took advantage of a karaoke segment on the scoreboard to really bring it home.

Instead of rocking along to Whitney Houston's "I Wanna Dance with Somebody" like everybody else ... the dude used his big moment to also mouth "Fire Nico" into the camera.

The camera operator quickly zoomed away after realizing what he was saying ... but the damage was already done -- and the fan was escorted out of the arena.

Even though the guy got kicked out for his anti-Nico antics, plenty of Mavs backers will defend the guy after the Doncic for Anthony Davis trade hasn't worked out so far.

A.D. suffered a left adductor strain in his debut on February 9 ... and is reportedly out for multiple weeks. Meanwhile, Doncic played his first game with the Lakers on Monday ... and recorded 14 points and four assists.