Dallas Cowboys running back Ezekiel Elliott, the N.F.L.’s leading rusher as a rookie last season, has been suspended for six games without pay for violating the league’s personal conduct policy.

The N.F.L., after a yearlong investigations, reached its decision after reviewing Elliott’s behavior during a six-day stretch in July 2016 in which his ex-girlfriend Tiffany Thompson accused him of assaulting her five times in Columbus, Ohio, where he played at Ohio State. Elliott was not arrested or charged because prosecutors concluded that Thompson’s statements conflicted with those made by Elliott and witnesses. But he remained subject to discipline by the league.

The N.F.L.’s letter to Elliott also cited an incident during a St. Patrick’s Day parade in March, when Elliott pulled down a woman’s shirt and exposed her breast, as reflecting “a lack of respect for women” and suggesting a “pattern of poor judgment and behavior.”

He can appeal within three days. If he does not appeal, his suspension will begin Sept. 2. If he serves the full six games, he can return to the Cowboys on Oct. 23.