NBA coaches are allowed to challenge a call once per game.

BOSTON – Dwindling final seconds. One-point game. In one of those elimination-slash-close-out NBA playoff clinchers. The basketball squirts out of bounds and one of the officials determines a defender last touched it.

But was that the right call? That team’s head coach huddles quickly with an assistant holding a tablet, signals for a timeout, then makes the now-familiar twirly-bird gesture, index finger high. The green light on the scorer’s table comes on. Referees head to a nearby monitor, the crew chief grabbing a headset …

The NBA hasn’t yet seen the Larry O’Brien Trophy or a trip to the Finals determined by the outcome of a last-minute coaches challenge. But it almost invariably will, either in this series or a future one. This is why it’s worth a review of what goes into the coach’s decision.

What: Details of the coach’s challenge

Prior to the 2019-20 season, the NBA introduced the challenge on a one-year trial basis. A year later, with some tweaks, the rule was made permanent. Here are the basics as it currently stands:

• Each team gets one challenge per game.

• To use a challenge, a team must call a timeout. If the challenge is successful, that timeout is restored.

• Three types of replay reviews can be sought: a personal foul against one of that coach’s own players; a called out-of-bounds violation, or a called goaltending or basket-interference violation. (In the last two minutes of the fourth quarter or overtime, game officials can review out-of-bounds and goaltending plays).

• The on-court crew chief makes the final decisions on foul reviews. The NBA replay center in Secaucus, N.J., makes the determinations of all other calls.

• To overturn the initial call, a review must provide “clear and concise visual evidence.”

Who: The eyes behind the bench

Typically, one or more assistant coaches or video tech staffers sit in the second row, iPads or other tablets in hand, right behind the head coach and lead assistants. Each home team is required to make available to those devices and to the locker rooms three video feeds: the home and visiting feeds, as well as a “coaches” feed. The “coaches” feed shows a full-court view without broadcast interference such as replays, commercials or multiple camera angles.

The second row of a bench’s coaching staff can provide key insights when deciding whether or not to challenge a call.

All that content goes through computer software either developed by the team or purchased from outside commercial vendors. One of the first widely used options came from a firm in Pittsburgh, Pa., DVSport Software. Video of plays arrives almost instantaneously.

That particular company provided replay and clips for coaching purposes, mostly for halftime and between-game usage by NCAA and NFL teams. But a March 2021 story in Basketballnews.com detailed a major shift in DVSport’s business:

In 2019, DVSport basketball account specialist Kenny Brown had an idea that the company could tailor some of their college sports products to NBA benches for coaches. Brown altered a couple products and headed to Las Vegas for NBA Summer League to pitch and demo his solution…

As Brown was preparing to demo the product, he got a notification that the NBA approved bench challenges for coaches. Craig Davis, DVSport’s director of team solutions, believed that the announcement was a revelation.

During the first season of challenges, NBA coaches would look to the JumboTron after dicey calls, waiting for replays that may or may not be shown. A year later, DVSport’s system became more in demand.

“When we went to Summer League, our initial thing was using this as an instructional method, and I don’t think we were getting a whole lot of traction down that track,” Davis said. “That was kind of the ‘eureka’ moment when they approved the challenges.’”

Eight teams initially signed up, including Dallas, Houston, Miami and both L.A. clubs. Over time, a majority of teams have bought in, too. Either using commercial software or custom-designed versions, tablets in the bench area are now ubiquitous.

The Rockets rely most of the time on what the tablet feeds reveal, coach Stephen Silas said. But he’ll sneak a peek at what’s available above, too.

“I’ll use the scoreboard,” Silas said. “Knowing that, obviously, when we’re home, they show every play that might favor us, but on the road, they won’t show hardly anything.”

Time is of the essence when a coach has to choose whether to burn a timeout. Silas recalled one such moment when an opposing player “loitered” in the lane before a free throw, trying to buy time while his coach decided to challenge or not.

“I tried to get the refs to call a delay of game,” the Houston coach said. “They didn’t, but they admitted afterward they probably should have.”

Washington coach Wes Unseld Jr. has made sure the person he entrusts to give him a thumbs-up or thumbs-down on a challenge feels no pressure.

“There are times when he’s not sure,” Unseld told NBA.com. “My whole thing with him is, ‘Tell me if you’re not sure, then I’ll make a call. If you’re adamant, then I’ll trust you.’ There’s no pressure and I’m not going to be upset if he’s wrong.”

When: The ‘art’ of the challenge

So we’ve dealt with the what and the who. The where and the why are no-brainers. That leaves the when of using a coach’s challenge.

Since each team only gets one – whether right or wrong, unlike in the NFL or MLB – each coach fashions his own hierarchy of circumstances for when in a game to challenge a call, dictated by the scoreboard, the foul counts on his players, the value of the possession in question and so on.

In the broadest terms, most coaches prefer to hang onto their challenges until later in games, when the value of a single outcome or possession is magnified.

“The general feeling is that a bad call early in the game, your team has time to make up for that,” said an assistant coach with one of the 2022 Finals teams. He requested anonymity because he wasn’t authorized to discuss the topic.

“When it comes to fouls, not all players are equal,” he said. “You’d rather not use your challenge in the first half, but if somebody like Giannis [Antetokounmpo] or Steph [Curry] picks up his third foul and it’s early in the second quarter, you might do it.”

Said Unseld: “Yes, you might say, ‘I’ll run the risk’ and use it then. But in general, you want to save that. There are so many plays down the stretch, final two minutes, that are not necessarily unclear but they can be open to interpretation.

“And if you can take points off the board or get points or get a possession, that can really change the complexion of a game late in the fourth.”

Consider a challenge of a defensive foul, called on your star who’s already in foul trouble. “If you get that overturned,” said our Finals team assistant, “that’s a home run.” It takes potential points off the board and spares a key player an additional foul.

Even turning a possession call into a jump ball can swing a game, Unseld said. “Having another opportunity late is of vital importance,” he said.

Wizards coach Wes Unseld Jr. reacts to a call during a game in November.

“You certainly don’t want to jump the gun, where you’re going to need a challenge later and you don’t have one,” Unseld said. “Last season, we did a pretty good job of using it appropriately. I never felt like, man, I really wish I had it but didn’t.”

Not Silas. “If I get to the end of the game and I haven’t used it, I’ll think, ‘Maybe I should have used it on that block/charge,’” he said. “I have kind of kicked myself at times.”

In the time between replay being instituted and the coach’s challenge being added and refined, NBA fans and viewers would see a parade of players twirling their index fingers in the air after plays they didn’t like. Now those reviews are dependent on their coach formally challenging them, but players and even some fans still do it.

“They’ll do it first quarter, first foul,” Unseld said, laughing. “Nobody fouls anymore – c’mon guys.

“They don’t know the rule or understand the rule change. I have to explain to them, ‘Look, I only have one. I trust that you’re right, but I’m not going to challenge it.’”

Late in a Finals game, with a championship potentially on the line? That’s when greenlighting the green light can change everything.

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Steve Aschburner has written about the NBA since 1980. You can e-mail him here, find his archive here and follow him on Twitter.

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