Coaches Challenge RuleA coach may call a timeout to utilize a Challenge to trigger a review of an F(1), F(2), offensive foul, or T result against his own team. Roll a 20-sided die. If the result is a 9 or lower, then the challenge is deemed successful (the call overturned), and the challenging team does not lose its timeout. If the result is 10 or higher, then the challenge is unsuccessful (the call not overturned), and the challenging team loses its timeout.For seasons from 2020 - 2023, a team will be allowed a single challenge in each game. Beginning with the 2024 season, teams will be allowed a second challenge if their first challenge is deemed successful.
My research has found that Coaches Challenges have been successful right around 45% of the time, thus the 9 or lower mark on the 20-sided die in order for a challenge to be successful for this rule. As a side note, I like to refer to optional rules like this as "reality rules." These are rules that aren't implemented for statistical accuracy purposes, nor as strategical or tactical options, but instead are intended to add a touch of "realism" to the game.
Full disclosure, I stole the term "reality rule" from the 1987 release of TSR's "Top Secret/S.I." roleplaying game, which implemented optional rules to make gameplay seem more "realistic."
Here is a link to the official NBA Coaches Challenge rule.