BOSTON (WHDH) - A Quincy man will be arraigned Monday on indecent assault and assault charges after police say he grabbed a woman from behind in Boston, forced her onto the ground, and began punching her while trying to take her clothes off late Saturday night.

And now a witness who says he stepped in to stop him is recalling the terrifying encounter with 7NEWS.

Officers responding to a radio call for an assault and battery in progress in the area of West Canton and Appleton streets around 9:30 p.m. arrested Amos Sykes, 35, on charges of indecent assault and battery on a person over 14 and assault and battery resulting in injuries, according to police.

An investigation determined several witnesses heard someone screaming and saw Sykes attacking the woman as he sat on top of her. The woman said she had been walking on Columbus Avenue when she was attacked from behind. The assault left her hospitalized with non-life-threatening injuries.

Sykes is expected to be arraigned in Boston Municipal Court.

Sam Holder told 7’s Chris Rogers he and his father were watching a football game when they heard the woman screaming for help and he made the decision to spring into action and stop the attack.

“We heard a shriek … so I came outside,” he recalled. “There was a lady laying there on the ground with her pants down, her panties down, guy was on top of her, other people were recording, and I have sisters, mothers, my whole family consists of mostly women, I just hit him.”

Holder said, “I just jumped in, I had no other choice. She was screaming and bloody, with her pants down around her ankles.”

The Boston Police Department is actively reviewing the facts and circumstances surrounding these incidents. Anyone with information is strongly urged to contact District D-4 Detectives at 617-343-5619 or The Sexual Assault Unit at 617-343-4400.

Community members wishing to assist in this investigation anonymously can do so by calling the CrimeStoppers Tip Line at 1-800-494-TIPS or by texting the word ‘TIP’ to CRIME (27463).

This is a developing news story; stay with 7NEWS on-air and online for the latest details.

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