“In the beginning, you’d call people out and tell them that something they said — locker room talk — wasn’t really funny,” Herzlich said last week, sitting on the living room couch of his New Jersey home. “There would be jokes or something denigrating to women. It would be the kind of thing they would never say in front of a woman, but since it’s all men, they thought it was O.K.”

It was not O.K. with Herzlich, and he had a specific reason.

Five years ago, his then-girlfriend and future wife, Danielle, sat him down and revealed something she had kept hidden. Danielle explained that she had been physically and emotionally abused by her father from the age of 9 until she was 15.

“It was very serious physical abuse,” Danielle said as she sat at home next to Mark and spoke publicly about the abuse for the first time.

Efforts to contact Danielle’s father, using several telephone numbers, were unsuccessful.

Danielle’s revelation was a thunderbolt to Mark, who in the years since has emerged as one of the N.F.L.’s more forceful advocates of raising players’ awareness of domestic abuse.

“I thought domestic violence was something rare that happened to other people,” he said. “Danielle’s story changed my entire outlook. Yes, the majority of men don’t commit violence against women, but men over all need to stand up to other men. Don’t just hold yourself accountable. Hold others accountable to treat women how they deserve to be treated.”