This marked the third time Allen has intentionally tripped an opposing player in the past year.
On Wednesday night in Greensboro, North Carolina, Allen was defending Elon's Steven Santa Ana late in the first half, with the Blue Devils ahead. Santa Ana drove past him on the baseline, and Allen stuck his right leg out, sending Santa Ana to the floor.
Allen was assessed a technical foul. He became overly emotional on the bench after he found out about the technical.
Duke coach Mike Krzyzewski said that after the game -- a 72-61 Duke victory -- Allen apologized to Santa Ana and Elon coach Matt Matheny during a meeting that the Blue Devils' coach set up for the four.
"I made a really bad play. I'm sorry to him, Santa Ana," Allen, a junior, later told reporters. "I'm sorry to the officials who had to call that. I'm sorry to my team. It was selfish and taking away from them. I'm not proud of that at all."
Krzyzewski called the incident "unacceptable" and noted, "The right thing to do was apologize in person."
After the technical, Allen went to the bench for the remainder of the first half, which Elon closed with an 11-2 run. He started the second half on the bench and returned to the game with about 16 minutes remaining, finishing the night with three points.
"That's a bad thing that he did tonight," Krzyzewski said in reference to Allen. "But the fact that then we had to be distracted by it all and his team, that added to it, and that's what he's really down about. He can't believe that he did that. For him, he would die for his team. Here, he let his team down tonight. That's a big punishment for him, and he knows it.
"These things happen, and I'm responsible for that kid. I love that kid. A lot of crap has happened to him and a lot of bad shots at him. That doesn't mean it's right for you to try and get back. Don't pay attention to it, but pay attention to the fact that you did something wrong and you let your team down."
Teammate Matt Jones said he tried to console the emotional Allen afterward.
"I love Grayson. He's my brother," Jones said. "We've been to battle. We've won a [national] championship together. We won plenty of games together. So there's nothing really you can say.
"I just gave him a really big hug, told him, 'I love you.' That's all that was, and let the silence kind of fill the void. There's nothing really you can say about it."
Allen spoke to ESPN at length before the season and expressed remorse about the two tripping incidents a year ago: one onLouisville'sRay Spaldingon Feb. 8 and another onFlorida State'sXavier Rathan-Mayeson Feb. 25.
"I think ultimately, I just made a mistake -- two mistakes -- and they were big ones and mistakes I regret," Allen told ESPN. "Ultimately, I let my emotions get the most of me -- in the heat of the moment, you know, did something that's unacceptable and not something I'm proud of. I think I'm a lot more mature now."
After the incident against the Seminoles on Feb. 25, the ACC said it would not suspend Allen, but it did reprimand the star Blue Devils player.
Duke athletic director Kevin White, in a statement to ESPN's Andy Katz on Wednesday night, said of the latest Allen incident: "The officials gave Grayson a T, and handled the situation immediately. We don't have any further comment at this time."
Asked whether he was worried about a suspension, Allen replied, "That's out of my control. I can't worry about something out of my control now."
Krzyzewski, speaking after Wednesday's win, defended how he handled Allen.
"I handle things the way I handle them," he said. "I think I've handled this correctly, and moving forward, I will continue to handle it correctly. I don't need to satisfy what other people think I should do. I'm a teacher and a coach, and I'm responsible for that kid. I know him better than anybody, and so to think that it's the last thing that's said about this to him is wrong.
"Obviously we will do more -- doesn't mean that you have to see it or anybody else has to see it -- but what he did tonight was right. That's what people do. They say they're sorry, they accept responsibility."
Allen had an opportunity to leave Duke after last season. Multiple NBA executives told ESPN that Allen would have been a first-round pick in the draft, but he decided to return to school for a variety of reasons. He said education was important, he wanted another opportunity to win a national title, and he wanted a chance to play some point guard.
Allen has struggled with foot injuries for much of this season. He is averaging 16.0 points per game -- down from 21.6 last season.
Information from The Associated Press was used in this report.