Zachary Angert went to Butler on Sunday to attend a Christmas party.

He ended up thwarting a would-be Grinch who police say snatched the purse from a woman and took off running, armed with a sizable knife.

“I acted on instinct,” said the 29-year-old Summit Township man. “I saw (the suspect) running and thought to myself, ‘I need to get this guy.’”

Aided by several other average Joes turned heroes, Angert helped foil the criminal caper but not before being stabbed in the hand for his trouble.

“They’re all to be commended,” said Butler Deputy Police Chief David Adam of the gang of good Samaritans.

Police arrested the suspected mugger, Zachariah A. Swann, 25, of Butler, who remains in the Butler County Prison on $50,000 bail.

Swann is charged with robbery, aggravated assault and two weapons charges for wielding the large fixed-blade knife.

Angert, owner of a family-operated printing business, on Wednesday spoke about his weekend role as crime fighter.

He was at the Monroe Hotel, where his wife works as a waitress, for her employee Christmas party. Shortly before 9 p.m., a woman’s screams outside interrupted the holiday spirit.

Angert caught a glimpse of someone running. He went out to take a look, thinking the commotion was nothing more than a fight.

“I heard a lady yelling,” he said. “She was saying, ‘Someone just robbed me.’”

He caught only a glimpse of the woman and would not know until later that it was Bernice Rasely of Butler, who also works at the Monroe Hotel and was there for the party.

Police said Rasely had gone to her car, apparently to get something, when Swann allegedly ambushed her after asking her for a light for his cigarette.

He snapped up her purse and took off in the 100 block of North Monroe Street, police said.

From a distance, the suspected crook, purse in hand and making a getaway gallop, soon came into Angert’s view.

“The adrenaline started to kick in,” Angert recalled.

Before he could process the old advice to look before you leap and think before you act, Angert leaped and acted.

“I was in a full sprint,” he said. As he made his 100-yard dash or so toward the suspect, he hatched a haphazard plan.

“I was thinking I was going to grab him or bear hug him,” Angert recounted.

Others nearby, meanwhile, were also running, just not as fast as Angert, at the suspected robber, who had since ditched the purse.

Seemingly out of nowhere, a car came up and cut off Swann — an intentional driving maneuver by another ordinary citizen wanting to help.

And it worked. It momentarily slowed down the defendant.

“He spun around to avoid the car,” Angert remembered. “He turned and faced me. That’s when I saw the knife.”

By then, however, it was too late to abort the plan.

“I had so much momentum,” Angert said. “I contacted him.” He hit his target with a shoulder.

Swann, in turn, started to swing and flail his right hand, which held the knife.

“I got stabbed,” Angert said. “I saw it hit me but I didn’t know how bad it was.”

The wound in the palm of his right hand, it turned out, wasn’t too bad, maybe a quarter-inch deep.

The defendant immediately assumed a defensive posture against Angert and two or three other men who joined in the confrontation.

“He was saying, ‘Back up. I’m going to kill you. Get away. Leave me alone. I’m going to stab you.’ Stuff like that,” Angert recalled.

“We kept telling him to drop the knife.”

Still swinging and waving the knife around to make his point, the suspect eased backward before turning and making another run for it.

He would make it only some 50 yards before the group of vigilantes, which had swelled to 10, maybe a dozen, had him cornered in a parking lot on North Elm Street.

Angert and another man took the lead and went all in, going for the purported bad guy.

“I punched him,” Angert said. The jab knocked off Swann’s eyeglasses. “I think it dazed him.”

Still, the suspect was not ready to give up his one advantage — the knife.

“He would not let go of that knife,” Angert remembered. “He had a death grip on that thing.”

The other man moved in and scored a spin around, takedown of the suspect. He held down Swann’s shoulders as Angert kept hold of his legs and a third man held his knife-wielding arm at bay.

The trio detained the defendant until police arrived.

It wasn’t until after Swann was taken away in handcuffs, that Angert was able to tend to his wound.

Some residents, pitching in to help in their own way, came out and provided him with peroxide and bandages.

“I’m so proud of how so many people banded together to help,” Angert said in trying to put Sunday’s events into perspective. He finished his reflection with one last thought: “I’m glad (Swann’s) off the street.”