Duke sophomore guard Grayson Allen is a captivating basketball player and hellacious competitor who this season has been enabled to behave like a punk of the highest order. Allen is worthy of blame, and the real scorn should reside with Duke Coach Mike Krzyzewski and Atlantic Coast Conference administrators for tacitly condoning Allen’s indefensible conduct.

Twice now, Allen has blatantly tripped an opponent. After the latest dirty play, the conference issued a public “reprimand” and the school said “the matter was handled internally.” In other words, the people responsible for disciplining Allen let him get away with it. Again. Allen has been branded a dirty player, and it’s hard to argue against the label. Is Coach K too busy shooting an ESPN commercial to do something about it?

Thursday night, in the final seconds of Duke’s 80-65 victory at Cameron Indoor Stadium over Florida State, Allen and Seminoles guard Xavier Rathan-Mayes engaged in back-and-forth nudging and minor shoving. As Rathan-Mayes broke to sprint down the court, Allen thrust his left leg behind him and tripped Rathan-Mayes, who tumbled to the court as the clock ran out. The referee did not call a foul.

“He wanted to keep playing physical,” Allen told reporters, including the Fayetteville Observer. “So I tried to walk away from it as he was grabbing me. We ended up tangling up and falling. It was really nothing.”

It was, of course, not nothing. There is a line between physical and dirty, and Allen bounded over it. Rathan-Mayes may have been banging Allen. That in no way justifies tripping him, although you could see why Allen might think it does. When he did it before, Krzyzewski acted like nothing happened.

On Feb. 8, Allen drove to the basket during a win against Louisville and ended up on his back. As Louisville broke down court, Allen stuck out his leg and sent Ray Spalding sprawling to the deck. Officials reviewed the play and tagged Allen with a flagrant foul; they would have been justified throwing him out of the game. Duke could have taken action to ensure Allen knew he had committed a dirty play, at the very least benching him until the first whistle. In Duke’s next game, against Virginia, Allen started and played all 40 minutes.

Krzyzewski had another chance now to send Allen a message other than, “You’re really talented and we’ve got a lot of injuries, so you can get away with playing dirty.” We don’t know if Krzyzewski punished Allen in private, with extra wind sprints or something of the sort. We don’t know what he did Friday as a rebuke, either. Krzyzewski should have suspended Allen for a game; even a half would have been better than managing the situation in incredibly small and lame fashion.

“The matter was handled internally and there will be no further comment,” a Duke spokesman said.

With Krzyzewski is unwilling to act in any meaningful way, the ACC should have taken action and suspend Allen for a game. The conference reviewed the play, but one wonders what it saw. This shouldn’t have been a tough call — a player had endangered an opponent the same way for the second time in a month. The conference turned feckless and let Allen off with a “reprimand.” Tsk, tsk — that should teach him.

For an example, they could have looked to how Maryland handled a player who could have seriously hurt an opponent. Earlier this month, Diamond Stone slammed Wisconsin forward Vitto Brown’s head against the court after a whistle. The next day, Maryland Coach Mark Turgeon suspended Stone, and the Big Ten reprimanded him. Stone’s misdeed was worse than tripping, but he also had no prior offenses.

Allen’s latest transgression surely will turn every last college basketball fan outside of Durham against him. He already fits college basketball’s most vilified archetype: the cocky, white Duke player. Unlike, say, J.J. Redick, Allen has done more than just play well to earn the scorn. Krzyzewski has only exacerbated Allen’s actions by enabling them.