NBA to test coaches replay challenge at Vegas Summer League

The NBA is planning to experiment with a coach's challenge system on referees' calls during Vegas Summer League, according to league sources.

Officials are still working on what mechanism coaches will use to trigger a challenge and what the parameters are but they will not use a flag, sources said. Both the NFL and Major League Baseball have coach challenge systems.

Over the last several years the league has used summer league and the G League to test out rule changes including adjusting goaltending rules, expanding officiating crews and even using a 4-point line.

The league has steadily increased the use of instant replay over the last decade, routinely adding the types of plays that can be reviewed and triggers that allow officials to go to the monitors.

No matter how the testing goes in Vegas, it is unlikely the NBA would adopt any new challenge rules for next season.