In the fourth quarter of a competitive Nov. 7 game against the Milwaukee Bucks, LA Clippers coach Doc Rivers was livid. He had asked for a review of an offensive foul call using the NBA's new coach's challenge. The officiating team refused to overturn its call despite what appeared to be video evidence supporting the challenge.

"I hate the rule!" Rivers said after the game. "Nobody wants to be wrong."

Less than two weeks later, a dramatic Clippers victory against the Oklahoma City Thunder was saved by a successful replay challenge that eliminated OKC free throws.

"I think the challenge is good for the league, after all," Rivers said with a smile.

In Anthony Davis' return to New Orleans last month, Los Angeles Lakers coach Frank Vogel lost a challenge on a foul call in the fourth quarter of a tight game. LeBron James approached ESPN commentators Mark Jones and Jeff Van Gundy with his own analysis, spoken loudly enough for the national TV microphones.

"When the ref makes that call, he don't never want to be wrong," James said. "They're never going to overturn it. Ever. Ever."

After Boston Celtics coach Brad Stevens "won" a challenge Sunday afternoon at Madison Square Garden -- only for the New York Knicks to still get credited for a basket on the play -- the mild-mannered Stevens was caught on television cameras giving his frank assessment of the challenge system.

"I'm done with these f---ing challenges," Stevens said. "This is unbelievable."

Welcome to the opening weeks of the NBA's coach's challenge. ESPN asked head coaches from almost half the league's 30 teams for their input on the challenge system. The views ranged from hostile to constructive, but there wasn't an endorsement to be found.

But for all the frustration and bewilderment the new rule has created across the league, don't expect it to go the way of the NBA's synthetic basketball.

"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."

Translation: Get used to it, coaches.

One reason the league office is pleased is that the challenge system -- which was tried in the G League before the competition committee approved it for the NBA this past offseason -- appears to lead to a greater number of correct calls. In other words, it's working, by the NBA's standards.

Through Nov. 30, coaches had made 174 challenges, and 75 resulted in overturned calls, according to research by ESPN Stats and Information -- a 43% success rate for challenges.

Those 75 corrections have not prevented coaches and teams from being annoyed by the way the rule has played out. On Tuesday, a fresh issue surfaced when the Houston Rockets quarreled with the refs after a James Harden dunk was incorrectly ruled a missed shot. After the game, officiating crew chief James Capers said no legal challenge by Rockets coach Mike D'Antoni was made, and therefore the call stood. Coaches have 30 seconds to challenge a call, according to Capers.

A number of coaches went on the record with ESPN regarding their opinions on the rule and its implementation.

"I'm not a big fan," Golden State Warriors coach Steve Kerr said.

"I don't like it," Miami Heat coach Erik Spoelstra said.

"I'm not super crazy about it," Toronto Raptors coach Nick Nurse said.

"I tend not to do it, because I don't understand it," said San Antonio Spurs coach Gregg Popovich, who was the last of the 30 coaches to attempt a challenge, which he won. "I don't get it, so I don't try."

"My preference is to let [the referees] do their job, and I'll do mine," Sacramento Kings coach Luke Walton said.

"I don't like it," Philadelphia 76ers coach Brett Brown said. "I don't like it."

Even Brooklyn Nets coach Kenny Atkinson -- who won his first five challenges -- isn't happy with it.

"I would check the 'no' box," Atkinson said.

Over the last few years, coaches and players have routinely expressed annoyance with the NBA's Last Two Minute Reports, which review the officiating at the end of close games. The reports include both correct and incorrect calls, but the coaches have remained frustrated because acknowledgement of the incorrect calls provided little satisfaction after the fact.

"This never-ending quest to get everything perfect, we're just chasing our tail."

Warriors coach Steve Kerr

The challenge system is a response to that concern, giving coaches, once per game, a way to have calls reviewed and overturned in real time. Yet, the coaches seem even more frustrated by the fix.

"I appreciate the NBA's willingness to try things and appreciate the fact that we don't stand still in this league," Stevens said. "I think the challenge is good in theory, but we just all have to realize that there's still a lot of judgment in those, too."

Stevens saw recently how a challenge could go wrong. In a celebrated matchup with the Clippers on Nov. 20, Celtics forward Jaylen Brown was called for a foul on a Paul George drive to the basket, infuriating the Boston bench. Stevens challenged the call. The national television audience could see that George had shoved Celtics center Daniel Theis -- committing an offensive foul -- as he began his drive. But the refs, by rule, were forced to ignore that part of the play because it occurred before the gather, which referees define as the start of a basketball move into a shot.

As with Harden's dunk, the result was not to get the whole call right, nor was that the goal. For now, the league has opted to keep the scope of the rule narrow to ensure the challenge system is implemented as consistently as possible.

"For this to be successful, referees have to have a demarcation line," McCutchen said. "What is tied to the play, and what is not tied to the play. Gathering the ball is tied to the play. ... Once we have a year's worth of data, then we can look at refining it and calibrating it."

One of the calibration points could be finding ways to reduce the amount of time spent looking at plays. The league says the challenge reviews are not taking longer than regular replay reviews (which are initiated by officials). Regardless, the challenge rule allows for two additional reviews per game, bringing the action to a halt at potentially its most exciting moments.

Several coaches mentioned they felt the games were dragging. In addition to frustration over how the rules are applied, delays are one of the first things coaches point out when asked about the new rule.

"I just think the length of time it is taking right now, it's lengthening the game," said Charlotte Hornets coach James Borrego.

"It slows the game down, that's what I think it does," New York Knicks coach David Fizdale said. "There's times you think you're right, and you're still wrong."

Said Kerr: "There's way too many stoppages in play. The challenges themselves are very confusing."

When and how to use the challenge rule have added to the many things that can keep coaches awake at night. Should it be used to prevent a star from landing in early foul trouble? Does it make sense to save it for a potential game-deciding call in the final moments? Which kinds of challenges are most valuable and likely to succeed?

With the rule comes new data to study. The price of a challenge is a timeout, requiring a new set of risk/reward calculations based on the score, the clock and the likelihood of a successful challenge.

"Those are all kinds of things that people are thinking out," said Utah Jazz coach Quin Snyder, who is on the competition committee that recommended the system be tried out. "It gets pretty complicated. The game moves pretty fast."

"I've been looking around the league, and it seems like everyone has a different philosophy," Minnesota Timberwolves coach Ryan Saunders said. "I think we're all learning."

Holding on to challenges until the end of the game is common, with half of challenges coming in the fourth quarter, according to the NBA -- and 15% of them coming inside the final two minutes.

Some calls are being overturned far more often than others. In five cases when defensive goaltending was called, the original call was overturned four times. In 22 challenges involving the ball going out of bounds, 15 calls were overturned, giving the ball to the team making the challenge.

Meanwhile, just 8 of 27 offensive fouls were overturned, as well as 12 of 28 personal fouls and 33 of 84 shooting fouls. In other words, it appears harder for coaches to get satisfaction on more debatable judgment calls.

Coaches, armed with more data and experience, will adapt. In big moments, they'll use every legal tool to win, including the challenge rule. But that might not change the other concern expressed by coaches: that the challenge system is not 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."

"We want perfection as fans, and I kind of like the imperfections," Atkinson said. "Maybe I'm different in that way, but that's just my thought."

"It's just another thing to focus on that's distracting," Spoelstra said. "We're all focusing on the wrong thing, I think. This is a beautiful game."

Despite such protestations, we should not expect the coach's challenge to go away. "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."

Atkinson, for one, is willing to reserve final judgment, even if he's skeptical now.

"Check with me in April," Atkinson said, "and see if that changes."

The NBA will be hoping that it does.