It's all spelled out in new court docs, obtained by TMZ Sports, in which the woman says she and Chung initially got into an argument over the way Chung was dealing with their son.

The woman said, per cops in the docs, that Chung had gotten upset with their son while at the ex-Patriots player's home in Norton, MA, and then drove the boy to her place in Milton.

Once he arrived, the woman said to cops that Chung told the boy, "Your mom's a piece of s***" ... and then pushed her to the ground when she got close to him.

Cops say the woman said she hit her butt, back and neck on the pavement as a result of the push -- and officers noted in the docs the ground was wet due to rain and her backside did have water stains on it.

The woman claimed, according to cops, that when she got up to confront Chung about the push, he struck her in the face with an open hand. She added that she then responded by hitting Chung in the face with an open hand.

Cops say the woman told them Chung then hit her again with an open hand, and then stole her cell phone.

Officers say the woman said Chung then got into his car, and before he drove off, he threw her phone, causing it to break.

Officers note in the docs the woman had "no physical marks" on her face, though they did say she complained of pain several times.

Cops say they eventually located Chung at his home in Milton and arrested him there.

10:55 AM PT -- Chung appeared in court Tuesday to face the charges ... and pled not guilty.

The judge released him on $10,000 bail. He's due back in court for a hearing on the matter in early January.