Updated

good Samaritan used his martial arts training and jiu-jitsu in coming to the resuce of a mother who was struggling to stop a stranger from snatching her baby in a New York City park.

Cellphone video shows Brian Kemsley pinning the man to the ground during the incident in Manhattan's Madison Square Park seven days ago. No one was hurt. Kemsley said the man appeared to have mental health issues.

The 33-year-old Kemsley said it all started when he heard a woman screaming as he was sitting on a bench in the park.

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Brian Kemsley, 33. (Brian Kemsley)

When he looked up he saw a man trying to take a baby in a stroller from the baby's mother, who was holding onto the stroller with a 4-year-old child in her arms. There were a couple of people trying to stop the person but he was refusing to let go of the stroller.

Kemsley told WPIX-TV the man was shouting “How do you know this is her baby? Why are you helping her? This could be my baby.”

Cellphone video captured what happened next, showing Kemsley grabbing the man from behind, wrestling him to the ground and then pinning him there.

"Here’s the thing, I don’t enjoy jujitsu, I don’t think training is particularly fun, but I have a lot of respect for it as it is absolutely essential in a street fight and self-defense," he said in an Instagram post about the incident.

Kemsley told Fox News Monday he kept the man on the ground for about 15 minutes, until park security arrived and place him in handcuffs.

He said the woman left the park with the baby and the other child but came back to thank him for intervening.

"I'm happy she did that," he said.

Kemsley said he has fought professionally in Muay Thai bouts.

The NYPD told Fox News police responded on Nov. 9 to a report of an emotionally disturbed person in the park around 3:24 p.m.

"The individual  was taken into custody and transported to Bellevue hospital for psychological evaluation," a spokesman said.

File photo - people dine outside Shake Shack in Madison Square Park in September. (Photo by Noam Galai/Getty Images)

Kemsley said he didn't think twice about helping the woman.

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“It's not a matter of stepping in, it's a matter of duty, when you see a woman and her child screaming,”  he told WPIX.