The NBA will implement a coach's challenge at the upcoming summer leagues and anticipates using the rule during the 2019-20 regular season as part of a pilot program, per a memo sent to teams this morning and obtained by 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. 

Both the league office and the NBA's competition committee, composed of coaches, front-office executives and players, are recommending the league's board of governors approve the rule for the 2019-20 season "on a trial basis," the memo says. 

"We anticipate this rule will be in effect in the NBA next season as part of a one-year pilot program," the memo states. 

When the league and its teams discussed the challenge concept at the general managers meetings in May in Chicago, there was some trepidation about allowing coaches to challenge called fouls, per sources who spoke to ESPN.com at the time.  Backers of a more expansive challenge system have apparently won that argument for now.  Coaches will not be able to challenge uncalled fouls.  Any attempt to expand the challenge rule into that area would result in a bigger, and likely longer, fight, sources said. 

Also in the memo:

The NBA during summer leagues will use the G League's "transition take foul" rule, which penalizes intentional fouls that stop fast-break opportunities but do not qualify as clear path fouls.  The fouled team will get one free throw -- to be attempted by a player of its choice from among the five in the game at the time of the foul -- and retain possession of the ball, the memo states.  There has been agitation in favor of the NBA adopting this rule. 

The NBA during the Las Vegas Summer League will experiment with a so-called "connected basketball" -- an official NBA game ball with a motion-tracking chip inside of it. 

Approving the proposed challenge rule for use in the 2019-20 regular season would require support from two-thirds of the league's teams in a formal vote of the board of governors.  The league will submit it to a vote before the full board on July 9. " Based on the feedback we have received, we expect it to be adopted," the memo says.