A dispute over attempts to buy alcohol for a man who was not of legal drinking age apparently escalated into an assault and fatal shooting early Friday outside a Maplewood nightclub.

Authorities say that Chou "Tony" Yang, 20, of St. Paul, was shot by a contracted, uniformed security guard at the Stargate Bar & Nightclub shortly before 1 a.m. The shooting occurred after Yang and at least five other men he was with reportedly chased the armed guard into the parking lot, said Maplewood Police Chief Paul Schnell.

The 28-year-old security guard, who has not been identified, apparently asked Yang, a year shy of the legal drinking age, to leave the nightclub, located at 1700 Rice St., after he — or one of his friends on his behalf — tried to buy an alcoholic beverage, Schnell said. According to fliers, the club was open Thursday night to patrons 18 and older.

Shortly after Yang was asked to leave, he and the group he was with swarmed the guard near the club's entrance and chased him. The guard apparently fell in the parking lot and was kicked and punched by the men. He then fired a shot, striking Yang, Schnell said.

Yang was taken by ambulance to Regions Hospital in St. Paul, where he died several hours later, Schnell said.

Yang was married with two daughters, said his friend Dennis Vang.

"We played football together and he's taught me a lot," said Vang, who said he considered Yang a brother.

Vang described his friend as a cheerful and funny person who was "always looking out for his family and making people in his life happy.

"He made a mistake, but that doesn't mean he's a bad guy," Vang added.

No one else was hurt in the incident, and as of Friday night, no one had been arrested, Schnell said.

When officers arrived at the scene, the group that had attacked the guard had already dispersed. Police are working to identify the attackers, Schnell said.

It's not known yet if the guard was pushed down, but it was clear to authorities based on surveillance video and witness statements that he was in distress, Schnell said. Authorities are still trying to sort through who was doing what at the time of the shooting, he added.

"In this particular case, we had numerous witnesses and the objectivity of video, which certainly helps," Schnell said.

Another armed guard was working at the club at the time, but wasn't nearby when the assault and shooting took place, Schell said. Other security personnel were inside the building.

The security guard, who works for JBM Patrol & Protection based in Madison, Wis., drove himself to the hospital for treatment of noncritical injuries, including scrapes and bruises, and he was later released. He is cooperating with police, Schnell said.

In a statement Friday, JBM management said that it was "saddened" by the incident and that it is cooperating with investigators.

The security officer who was attacked joined JBM in 2012, and has undergone "extensive tactical, firearms and use-of-force training, and has an exemplary employment record," the company said. "While this morning's incident is a tragedy, our officer followed the proper procedure when his own life was threatened."

The Maplewood Police Department and the state Bureau of Criminal Apprehension are investigating the case, which eventually will be sent to the Ramsey County attorney's office for consideration of charges, Schnell said.

"In any instance like this, the use of force like this is going to have to be legally justified," Schnell said.

In 2011, a 21-year-old man was sentenced for stabbing and slashing three men with a box cutter outside Stargate. At the time, off-duty Ramsey County sheriff's deputies were working security at the club and were called to break up the fight in the parking lot.