According to the incident report -- obtained by TMZ Sports -- Young's 20-year-old ex-girlfriend stated she went to his apartment in Athens around midnight so they could discuss their relationship.

The ex said the conversation grew heated after she learned he was on the phone with another woman ... and claimed there had been infidelity in the relationship.

The woman stated Young "grabbed her left arm near her bicep and tricep and physically pulled her out of the room" during the spat ... and used derogatory terms toward her before locking himself in his bedroom.

The woman told cops she began grabbing his belongings and answered a phone call from a friend ... which prompted Young to come back out and grab her from behind, pick her up and squeeze her torso and abdomen "very hard."

The responding officer noted a bruise and discoloration on the bottom right side of the woman's chest where it meets the abdomen ... as well as redness on her right flank.

After taking the woman to a nearby hospital for treatment, cops made contact with Young at his apartment ... and he initially said nothing had happened. After talking further, the 22-year-old said the two spoke about their relationship ending -- and when the argument intensified, he escorted her to the front door.

Cops say he denied grabbing her and any injuries observed did not come from him ... while noting he was "very closed and gave very short closed answers" during the interview. Young was arrested on probable cause based on the "totality of the circumstances" and "physical evidence of injury" to the woman.

Young -- who transferred to Georgia from Miami in December -- has appeared in four games for the Bulldogs this year ... including Saturday's game against Auburn. He has 11 receptions for 149 yards and two touchdowns.

In a statement given to ESPN ... the University declined to comment. Young's attorney, Kim Stephens, told the outlet he did not make physical contact with her "in any way that could ever be considered a crime."