Zach Collins better get ready to open his wallet ... 'cause it's likely going to cost him big time for flipping off a referee after being ejected from Friday's game.
Here is the deal ... the Sacramento Kings dominated the Spurs in San Antonio with a 140-113 victory ... but it was what happened while the game was still in reach that's making headlines.
Zach -- the Spurs' power forward -- flew off the handle after he was ejected following a series of fouls ... and he got so pissed over it, he flipped referee Michael Smith the bird.