The treatment of players involved in domestic violence cases has become an inflammatory issue for the N.F.L. after a video emerged showing Ray Rice, at the time a Baltimore Ravens running back, knocking his fiancée unconscious. Amid heavy criticism, Commissioner Roger Goodell acknowledged that his initial two-game suspension of Mr. Rice was insufficient and that the league had fallen short in its handling of domestic abuse. In light of the Rice case, the N.F.L. has promised to overhaul its personal conduct policy.

Long before the Rice controversy, however, the Merling case served as an example of how N.F.L. players can receive lenient treatment not only from local law enforcement agencies but also from a league that has taken an inconsistent approach to domestic violence — despite a pledge in 2007 to strictly enforce its personal conduct policy. Through interviews with Ms. Lennon and a review of documents obtained through public record requests, The New York Times found a pattern of continuing harassment by Mr. Merling — while he continued to play in the N.F.L.

Image When sheriff’s deputies arrived at Ms. Lennon's home, they found her with redness and swelling on her face and a cut on her lip. Credit... Broward County Sheriff's Office

Tony Sparano, the Dolphins’ coach then, told reporters “it really is a league situation right now, the league is handling this.” Mr. Merling was never suspended by the league or the Dolphins, and he returned to the field in 2010 after his arrest. “He went right back into minicamp,” Ms. Lennon, 25, said in an interview last month in Columbia, S.C., where she now lives. “I saw pictures of him stretching.”

He played parts of four more seasons for the Dolphins, the Green Bay Packers and the Washington Redskins. Ms. Lennon, speaking publicly for the first time about her experiences, said she had never been contacted by the league or any of the teams.

“I wasn’t surprised,” she said. “The players are the only ones they care about.”

Ms. Lennon said the harassment continued into this year, including threatening text messages and angry outbursts that left dents in her car and front door.

In an email, an N.F.L. spokesman, Brian McCarthy, said: “We would not be aware of allegations that may have been made and determined by the police to be unfounded or which did not result in any formal police action unless the player or alleged victim notified us. Typically, the police do not notify the N.F.L. independently.”