For Sarah Dodds-Brown, the shock of being singled out for a racist attack was compounded by the fact that no one stepped in to help her. She was riding the train to work one morning in mid-January when a man began elbowing her in the back. When Ms. Dodds-Brown, who is black, asked him to stop, he said, “Obama’s term is over.” Then the man, who was Asian-American, delivered an angry rant that included a comment about “self-righteous slaves.”

“I wouldn’t have expected somebody to confront him, necessarily,” she said. But even someone making eye contact with the man, she said, would have sent the message that his behavior was unacceptable.

Harassment can be more traumatic when no one steps in to help, Ms. May said, and people who have experienced it are more likely to wish a bystander had spoken up than that police had gotten involved.

Two fellow passengers stepped in to help Ms. Heir after the incident on the L train. One woman tapped her on the shoulder and asked if she was all right. “That meant something,” Ms. Heir said, “because when you’re a minority, you’re so used to just experiencing things on your own.”

Another woman reported the incident to a police officer at a subway station.

Anyone who witnesses or experiences harassment on the subway can report it to the city’s human rights commission by calling (718) 722-3131. Communities Against Hate, a partnership of 11 civil rights organizations, operates a hotline at 844-9-NO-HATE (844-966-4283), where people who have been harassed can get information about resources like legal services and counseling. Hollaback and other organizations offer bystander intervention training to help people learn what to do if they see someone being harassed.

Ms. Dodds-Brown reported what happened to her on the subway to the Documenting Hate project, a group of organizations — including The New York Times opinion section — tracking hate crimes and harassment since the election. She also posted about the incident on Facebook and talked to her children and their teachers about it. She wanted people to understand how to protect themselves and others, she said. “We actually all have a responsibility to create the society we want.”

If you have experienced, witnessed or read about a hate crime or incident of bias or harassment, you can use this form to send information about the incident to This Week in Hate and other partners in the Documenting Hate project. The form is not a report to law enforcement or any government agency. These resources may be helpful for people who have experienced harassment. If you witness harassment, here are some tips for responding. You can contact This Week in Hate at weekinhate@nytimes.com.