The NBA's challenge system has been frustrating to many coaches during its first season of implementation.

Through Nov. 30, coaches had made 174 challenges, and 75 resulted in overturned calls.

"I'm not a big fan," said Steve Kerr.

Erik Spoelstra, Nick Nurse, Brett Brown, Kenny Atkinson and Gregg Popovich all have gone on the record to voice similar sentiments.

"We're very pleased with how a very difficult concept and rule has been implemented," said Monty McCutchen, the NBA's vice president of referee development and training.

"There have been some growing pains, but overall we're very happy."

"We get the apprehension," NBA president of league operations Byron Spruell said. "We're working through it. The engagement and feedback have been good. We haven't been surprised that we're getting such feedback, and we've welcomed it. ... It's not perfect, we know that."

Kerr expressed a belief that he doesn't believe it is good for the game.

"I don't think it's adding to the game," Kerr said. "This never-ending quest to get everything perfect, we're just chasing our tail. The fact is the referees have an enormously difficult job. You can watch a replay and two rational people can argue. I think we're trying for the impossible."