A woman in a Walmart in Texas last week who took photos of a man pushing a shopping cart with his daughter’s hair wrapped around its handle helped touch off a debate about when, or if, a bystander should intervene when a parent harshly disciplines a child in public.

The woman, Erika Burch, was with her husband, Robert, in the store in Cleveland, Tex., about 45 miles north of Houston on Sept. 19 when they spotted the girl walking extremely close to the cart. Her head was leaning at an odd angle as the man dragged her alongside the cart by her hair, Ms. Burch said in an interview.

Mr. Burch, 44, said the girl, who the police said was 5, was crying: “Please stop! I won’t do it again.” He added that she was “just begging the man to let her go.”

Ms. Burch, 25, intervened.

She said she spoke to the man three times to try to get him to stop, each time raising her voice. Ms. Burch said the man told her, “I grew up just fine,” and began cursing at her. She called 911, and a police officer who was in the store about a shoplifting case was there within minutes.

On its Facebook page, the Cleveland Police Department said a joint investigation was underway with Child Protective Services. Witnesses were interviewed and reports were taken, the police chief, Darrel Broussard, said in an email.

“We do not condone the father’s actions in this incident, but we must gather all the facts and evidence,” he wrote, adding that the father let go of the girl’s hair “pretty quickly.”

“There have been forensic interviews conducted with county child advocacy group, and digging into the past behavior and history of the family (none found),” the chief wrote.

No charges have been filed, and the man was not identified by the police. The chief said that “many intervention plans” were in place and that the child was “doing great,” adding that the family has “a very strong mother.”

Since Ms. Burch posted her story on Facebook, it has been shared more than 242,000 times and was reported by numerous news outlets. It was only after she intervened at the store, she said, that other shoppers thanked her. She said some people later sent her Facebook messages that the couple, who have four children, ages 2 to 7, should have minded their own business.

But Mr. Burch said the circumstances demanded action. “This is what is wrong with America today,” he said. “Everybody’s too scared to get involved anymore.”

So what should observers do in situations like this one? We asked the experts.

Is it my business to say something?

• Dan Duffy, president and chief executive of Prevent Child Abuse America, said his organization is a firm believer that “if you see something, say something.”

• Do not wait for the situation to deteriorate before getting involved, said Darleen Simmons, a public health educator with Saint Paul-Ramsey County Public Health in St. Paul, and the lead trainer for the Wakanheza Project, which teaches strategies to defuse stressful situations. (Wakanheza is the Dakota tribe word for child; its English translation is sacred being.)

“If you wait for something to get worse before doing anything, it definitely can get worse and then it becomes harder to connect and be of help,” she said.

• Folusho Otuyelu, an assistant professor of clinical social work at Touro College Graduate School of Social Work in Manhattan, said, “Others may not be brave enough to intervene but are thinking someone should get involved.”

The person intervening may feel alone but really is not, she said.

Should I call the police?

• Chris Newlin, executive director of the National Children’s Advocacy Center, said people commonly call 911 if they see a fire or a crash, so why should cases of child endangerment be different?

“If someone is being abusive to a child in public, just imagine what happens behind closed doors,” he said in an email.

• Dr. Jeffrey Gardere,a clinical psychologist and a professor of behavioral science at Touro College of Osteopathic Medicine in Manhattan, said that if you believe the child is in “imminent danger,” you can make an anonymous call to the police.

“You may feel guilty that you may be getting that parent in trouble, or that you may be making a mistake and misinterpreting the situation,” he said. “However, think about how inaction can lead to the injury, danger or death to the child. Now think about that guilt.”

• Other experts cautioned that involving the authorities right away might cause the situation to escalate. The parent might be frustrated or having a bad day and not necessarily be abusive.

“You do need to acknowledge the right of parents to discipline their child within limits,” Dr. Lolita M. McDavid, medical director of child advocacy and protection at Rainbow Babies and Children’s Hospital, the pediatric hospital of University Hospitals Case Medical Center, in Cleveland, Ohio, said in a email.

If you believe a child is “truly being hurt or assaulted, you do need to step in and do something about it,” she said.

In that case, be very firm with the parent, but if that person confronts you, alert a security guard or the police immediately. “You have to be safe yourself,” Dr. McDavid said.

That is not an unfounded concern. In 2011, a mother on a Philadelphia bus who was angry at being criticized by a passenger for spanking her child made a phone call, and two accomplices arrived and fired on the bus with an assault rifle and a pistol right after she left, The Philadelphia Daily News reported. No one was hurt.

Ms. Burch said the thought crossed her mind that the man in Walmart might have a gun. She said that she watched closely for any sudden movements, but that she would not relent.

“He would have to shoot me right there,” she said.

Am I legally obligated to intervene?

Mandated reporters, such as teachers or doctors, are required to report suspected child abuse, but ordinary citizens are free of that obligation, said Randall M. Kessler, a former chairman of the American Bar Association’s Family Law Section, who has a law practice in Atlanta.

“While some might argue there’s a moral or ethical responsibility, we do not as a society criminalize a failure to report a crime,” he said in an email.

Some states have “good Samaritan laws” that protect those who intervene from civil claims if they acted in good faith.

How should I approach the situation?

• Avoid being angry, stern or confrontational, Professor Otuyelu said.

Be warm, friendly and concerned. Speak in an even and soft tone and ask politely if the person needs help. Gently but firmly point out that the child could get seriously hurt and that the person’s behavior needs to stop immediately.

• Collect yourself before you talk and withhold judgment, Ms. Simmons said.

“It really starts with no one as a parent wants to be told we’re doing something wrong or we’re a bad parent,” she said. “That’s a recipe for something to blow up in your face.”

What do I say?

• Professor Otuyelu suggested: “Hello, I don’t mean to get into your business or tell you how to parent, but I noticed that” and fill in the sentence with what you observed.

• Mr. Baker recommended: “I remember when my children were that age. They can be a handful. Do you need any help?”

• Dr. McDavid recalled a shrieking child and a screaming mother waiting to check out at a grocery store: “I said to them ‘Hey, are you O.K.?’ I said to the child, ‘Can you stand there quietly while we wait in line?’ They both calmed right down.”

• Ms. Simmons said sometimes you have to act in the moment. She recalled an airplane passenger seated near a child who was crying and acting out. The passenger made a hand puppet out of an airsickness bag to distract the child and it worked, she said.

“If you bring a genuine care and desire out of love and respect, people will get that,” she said.