The group of women stopped some 20 feet away from the couple.
"Hey! Hey," shouted one of the women. "You want me to call the police?"
"Don't worry. I have everything under control. Sorry about that," the boyfriend responded, but his abuse continued.
As the victim pleaded with her boyfriend to leave her alone, one of the women cringed and covered her ears.
"Excuse me," yelled another of the women. "Take your hands off her! You know, somebody went to call the police, so I wouldn't take her anywhere."
We interrupted the intense scene and informed the women of our hidden camera experiment. They felt good about their group effort, despite their trepidation.
"I definitely think I was weighing in my mind my fear and what was the right thing to do," said Beth Perlman.
Adrianne Meisler said, "We just knew we had to stay there until the police arrived. That was enough to do in the situation to ensure her safety."
Over the course of our experiment we noticed a pattern of mostly women stepping in. We wondered if only women were going to intervene.
Our answer came as a tall jogger approached the fighting couple.
Suddenly, the boyfriend kicked her, just as the jogger ran by. The jogger reacted immediately.
"Hey, hey! Leave her alone!" the man yelled loud enough to be heard across the park.
When the boyfriend stood up to him, the jogger cut him off.
"In no situation do you kick a girl!" he told the abuser.
Concerned the confrontation might escalate, "Primetime" correspondent John Quinones left the control van to inform the runner about our experiment.
While a majority of passersby kept right on going, we wanted to know why David Young, the jogger, made the split-second decision to get involved.
"You make your choices," Young said. "I mean, if I was standing, you know, 40 feet away and had a cell phone, maybe I would have made a different decision. But I was right there, he had just kicked her, so you do what you have to do."
Right after the confrontation, Young said his pulse rose from about 135 beats per minute to around 170.
"So the adrenaline kicks in," he said.
Young was one of few men who intervened with our fighting couples. What kept the men from intervening?
"It was almost as if the men anticipated that there would be some sort of physical fight that would occur," Keating said.
As it turned out, race may have been a factor in terms of who intervened, and with which couple. Over two days of shooting, we noticed that women seemed less inclined to intervene when the abusive boyfriend was African-American and the victim white.
"African-Americans are stereotypically more aggressive than Caucasians," said Keating. "They [passersby] may have been more hesitant for that reason."
The people who intervened with our interracial couples told us that any fear they felt -- and some said they were very scared -- was outweighed by an overwhelming desire to help someone in trouble.
"The reason why people help is complex," said Keating. "We help not only to get a victim out of distress, but we also help to set the world right. Most of us … will work toward that goal and will put ourselves at risk to accomplish that goal."
"When I was able to get [the victim] away, I felt really empowered," said Underwood, smiling and raising her fists triumphantly.