Warriors head coach Steve Kerr clearly does not buy into many of basketball’s unwritten rules.

“I’m on a one-man crusade to dispel these idiotic NBA rituals,” Kerr said.

Here was the situation: Warriors guard Shaun Livingston took a mid-range jumper with about three seconds left in Game 1 of the NBA Finals on Thursday night, and his team ahead 122-114. The shot clock was about to expire. So, as Kerr instructs his players to do, Livingston launched.

Cavaliers center Tristan Thompson took exception to this, because the outcome already was decided. Thompson contested the shot with a high elbow, received a flagrant foul and was ejected. This led to the skirmish between him and Draymond Green.

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Thompson contended Livingston violated an unwritten NBA rule, suggesting teams comfortably ahead should let the shot clock expire in the final seconds.

“That was some bull—,” Thompson said later of Livingston’s shot.

Kerr, standing in a hallway after his news conference and speaking to three Bay Area reporters, vigorously disagreed.

“If there’s a shot-clock differential, you shoot the ball,” he said. “The game is telling you you’re supposed to shoot the ball. And if anybody is offended because you’re playing the game the way the clock and the rules are telling you to play, then I think that’s silly.

“If the shot clock is off, then you run the clock out. If the shot clock is on, you take a shot. I don’t know why there’s any ritual that says you’re supposed to stop playing. We’re going to shoot. We’re not taking a turnover.

“I’ve told our guys that for four years. We don’t take turnovers at the end of the game. You shoot, the other team gets the ball and they can run it out or do whatever they want to do.”

Thompson, naturally, saw it differently.

“Shaun is a smart player, he’s been in the league a long time,” Thompson said. “I played with Shaun. He knows. But he shot the shot. Maybe he wanted to increase his points-per-game, I don’t know.”

Cavs head coach Tyronn Lue asks his players not to shoot if Cleveland is ahead in a similar situation. That probably shaped Thompson’s reaction Thursday night.

At the same time, Lue sought to defuse any lingering tension.

“For us, when the game is out of hand and we know a team can’t score and win, we let the clock run out,” Lue said Friday on a conference call. “But their policy is to shoot the ball. It’s no big deal to me. Whatever.”

Ron Kroichick is a San Francisco Chronicle staff writer. Email: rkroichick@sfchronicle.com Twitter: @ronkroichick