Ionut Adrian Tanasoaia surrendered to police and will be in custody for 29 days while he awaits trial. He is accused of beating up Hardy in a bar in the southern Romanian city of Giurgiu on Saturday night.
Hardy died shortly after surgery Sunday in Bucharest. The 23-year-old player sustained severe head injuries and was in a coma when admitted to the hospital in Giurgiu, where he played for CSS Giurgiu and was celebrating a victory over rival Dinamo Bucharest.
Hardy was punched after he playfully put his cap on a woman's head, prosecutors said. They added that the woman's boyfriend objected to the gesture, and Hardy tried to show he didn't understand Romanian. Tanasoaia then allegedly punched Hardy on the chin and he fell to the ground.
A preliminary autopsy revealed a massive hemorrhage and broken skull. Giurgiu county hospital spokeswoman Elisabeta Bene said Monday that doctors initially suspected Hardy was in a coma because he had been drinking. She said his condition deteriorated a few hours later and he was transferred to a hospital in Bucharest, 38 miles from Giurgiu.
"We are concerned by the violent circumstances surrounding the death of this U.S. citizen, and will pay close attention as the investigation progresses," the public diplomacy department of the U.S. Embassy said in an email to The Associated Press.
Romania's health ministry Monday ordered an inquiry to determine whether emergency procedures had been followed.
Hardy, who arrived in Romania in August, was a guard at Sacred Heart from 2006 to 2010. He averaged 12.5 points in his last season.
"This is not just about a basketball player, but the person as well," Sacred Heart coach Dave Bike said in a statement Sunday. "It transcends what happens on a basketball court. We feel tremendous sadness and loss for Chauncey's family and those who were close to him."