According to a Germantown Police Dept. report, the interaction between the teenager and the Memphis Grizzlies point guard happened at Houston H.S. in Tennessee on Sept. 22 at around 7:10 PM.

In the docs, police say at an after-school volleyball game, Morant's sister -- who attends Houston H.S. -- got into a verbal argument with another student.

Witnesses on the scene, according to the docs, told officers both parties had called each other "bitch" -- prompting Ja's sister to contact Ja about it all.

A short time later, cops say Ja, Ja's mom and dad, Ja's baby daughter and "a group of" adult males all came into the gym together. According to the documents, most of the group -- excluding Ja's father -- went to confront the student in the stands at the game who had been quarreling with Ja's sister.

"Which one of ya'll called her a bitch?" Jamie Morant, Ja's mother, allegedly said.

Cops say in the docs they told Jamie she "can not come upstairs and confront the students and they did not need to make a scene at the school." But, officers say while they were talking, one of the men with Ja moved past police and walked toward students.

According to the report, witnesses on the scene said the man slapped a phone out of a student's hand who had been attempting to take a picture of Ja in the stands ... and then said, "I don't care about none of that, I will beat y'alls ass."

A witness later said that man "was about to pull a gun" -- though cops on the scene said in the documents they never observed a firearm during the incident.

Police say everyone eventually left the gym without further problems.

The next day, cops say the mother of the student who had been in the spat with Ja's sister wanted to press charges against all parties, including Ja, for intimidation and harassment. Cops say Jamie Morant also wanted to press charges against the student who had been in the tiff with her daughter for threats and intimidation.

Cops investigated Ja for simple assault, intimidation -- no physical contact, but no charges were ever filed.

The mother of the student, meanwhile, tells TMZ Sports her son was also investigated, but did not end up being charged either.

According to the police report, the Grizzlies' head of security -- ID'ed as Kevin Helms in the report -- came to the school to discuss the incident with authorities. Cops say Helms "was asked to give a verbal trespass warning to all parties per the request of the Principal."

We've reached out to the Grizzlies for comment on the situation, but so far, no word back yet.

The situation was one of at least three times in the last calendar year that Ja has been investigated by cops. In the summer, police probed into allegations that he roughed up a teenager during a pickup basketball game at his home. Earlier this week, cops looked into video he posted where he brandished a gun at a Denver-area nightclub. He was not charged in either incident.

Ja -- a 23-year-old, two-time All-Star who's considered one of the best young players in the NBA -- is currently away from the Grizzlies in wake of the gun video.