Remember when the little Atlanta Hawks stunned the Boston Celtics in an NBA Cup game earlier this month?

Apparently, Atlanta’s lineup has raised a red flag with the NBA.

The NBA fined the Hawks $100,000 for violating its player participation policy in their win over the Celtics at TD Garden on Nov. 12, noting that star guard Trae Young was healthy enough to play and should not have been ruled out.

“After an investigation, including review by an independent physician, the NBA determined that the Hawks held Young out of a game in which he could have played based on the medical standard in the policy,” the league said in a statement. “The organization’s conduct violated its policies, which are intended to promote participation in the NBA regular season.”

At first glance, it’s strange that the Hawks would rule out their star player for perhaps the biggest game of the young season so far: a road game against the defending champion Celtics in their first game of NBA Cup group play. (The Hawks ruled Young out with “right Achilles tendonitis” despite him having two full days off for the Nov. 12 game. It’s the only game he’s missed so far this season.)

Atlanta may have had the motivation to give Young a breather; just eight days earlier, he had one of the worst games of his career against Boston, scoring just two points on 1-of-10 shooting in a 30-point home loss to the Celtics.

Sure enough, the Young-less Hawks thrived without their All-Star guard in that Nov. 12 game, upsetting the Celtics 117-116 thanks to stellar performances from Dyson Daniels and Jalen Johnson.

That decision to sit Young will cost Atlanta, but the team now controls its own fate in the NBA Cup group stage; if the Hawks beat the Cleveland Cavaliers on Friday, they will win Group C and advance to the quarterfinals.

If Atlanta loses to the Cavs, Boston can win the bracket by beating the Chicago Bulls in NBA Cup action on Friday night. Celtics-Bulls tipoff is scheduled for 8:00 PM ET on NBC Sports Boston.