The NBA's new challenge rule has been met with mixed reactions. Some are in favor of the idea, while others are not. Boston Celtics head coach Brad Stevens appears to be in the camp of those who are opposed.

In the latter stages of Sunday night's game against the Knicks, Stevens challenged a call. Grant Williams fouled Julius Randle on an and-1. After a review, it was determined that Williams didn’t commit a foul. However, the refs ruled that Randle was already shooting, so his basket was counted.

Stevens was not pleased with the verdict. He leaned back in his chair and voiced his opinion, appearing to say: “I’m done with these f—ing challenges. This is unbelievable.”

Though Stevens was frustrated with that particular ruling, his Celtics went on to defeat the Knicks, 113-104. Jayson Tatum led Boston in scoring with 30 points, seven assists and six rebounds. Jaylen Brown added 28 points, while Kemba Walker finished with 16 points and 10 rebounds. The Knicks were leading by nine in the second half, but the Celtics managed to rally for the win behind a 17-2 run in the fourth quarter.

Stevens was pleased with the win, but he admitted his team needs to start games better:

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“At the start of the game we didn't come out with the stuff,” Stevens said following Sunday's game, via ESPN. “But it's good that we can turn it to that level, and we had a couple of great ball pressure plays there at the end of the game that helped us create some separating. But I don't think we can keep going into games and giving up 85 points with 10 minutes to go and expect to be successful.”

The Celtics will be back in action on Wednesday night, when they'll serve as hosts to the Miami Heat. Tip-off inside TD Garden is set for 7:30 p.m. ET.