There are major changes coming to the NBA's replay review system next season. The league announced that they will implement a Coach's Challenge system one a one-year trial basis in the 2019-20 season. 

The NBA Board of Governors today unanimously approved two changes to instant replay rules. The first change is the introduction of a Coach's Challenge to trigger instant replay review of a limited set of matters. A version of the Coach's Challenge that has been in effect in the NBA G League for the last two seasons and is being used at MGM Resorts NBA Summer League 2019 will be adopted in the NBA on a one-year trial basis during the 2019-20 season.

The second change enables the NBA Replay Center (in addition to the on-court referees) to trigger instant replay in certain circumstances. The process, which was successfully tested at MGM Resorts NBA Summer League 2018 and is being used again at this year's event, will be implemented for the 2019-20 NBA season. 

According to a report from Shams Charania, the system will not use physical flags such as they use in the NFL, but rather the challenge would be initiated via a signal from the coach. 

Additional reporting from Adrian Wojnarowski of ESPN indicates that coaches will be allowed to challenge a variety of calls, including foul calls, which is perhaps the most interesting aspect of this plan. Whereas out-of-bounds and basket interference calls are objective, many foul calls are quite subjective. 

This is the first time in NBA history that coaches will have the ability to challenge calls. The plan has undergone testing during Summer League in Las Vegas and last season in the G League. 

Last month, ESPN's Zach Lowe reported on further details of the plan ahead of its implementation during Summer League. Coaches will get one challenge per game, and will lose it regardless of whether or not they are successful. In addition, Lowe noted that the crew chief will have final say in challenges involving foul calls, while all other decisions will be made by the replay center. Via ESPN:

Coaches will get only one challenge per game, whether it is successful or unsuccessful, according to the memo. They can use it to challenge only called fouls, goaltending, basket interference and plays when the ball is knocked out of bounds, the memo says. The NBA has tested this version of the challenge system in the G League over the past two seasons.

Coaches must have a timeout remaining to use a challenge. The team must call a timeout immediately after the event it would like to challenge, and the coach must "twirl his/her index finger toward the referees" to signal for the challenge, the memo states. If the challenge is successful, the team retains the timeout it used to stop play. If the challenge is unsuccessful, it loses that timeout.

The crew chief among the referees will determine the outcome of challenges involving called fouls. The NBA Replay Center will decide all other challenges. Any technical flagrant fouls that occur during or "immediately after" the call being challenged will stand regardless of the outcome of the challenge, the memo says.

It will be fascinating to see how this new plan works, especially in the early stages as coaches get used to their new tool. With how fast basketball is played, coaches will at times only have a few seconds to decide whether or not they want to challenge a play, and may not have replays at their fingertips to influence their decision like coaches in other sports have. 

Plus, with only one challenge at their disposal, will they try and save it for a crucial moment late in the game, or use it early on a call they know they can overturn? And then there's the timing issue on the league side. How long will these replay reviews -- in particular foul calls where it's a more subjective matter -- take? How much will they interrupt the natural flow of the game?

There will probably be some growing pains with this new process, and it will be interesting to see how it all unfolds next season.