"The evidence did not support a finding that Foster violated the NFL's personal conduct policy in connection with the Tampa incident in November 2018," the NFL's statement said.
The former first-round pick will not be suspended. He has been removed from the commissioner's exempt list and reinstated to Washington's roster.
Foster was arrested and charged with a domestic violence misdemeanor in November. The San Francisco 49ers subsequently released him. Washington claimed him on waivers, but the league then placed him on the commissioner's exempt list while it investigated. The charges against Foster were dropped in January.
"I accept the NFL's decision and want to say that I am truly sorry for my past actions and the people who may have been hurt by them," Foster said in a statement, according to ESPN's Adam Schefter. "Going forward, I will follow the plan outlined for me and work hard to earn back the trust of my teammates, the NFL, NFL fans, and the community."
Foster's ex-girlfriend, Elissa Ennis, said the linebacker slapped a phone out of her hand, pushed her in the chest area, and slapped the side of her face with an open hand at the team's hotel.
After reviewing video from the hotel, the NFL concluded Foster did not violate the league's personal conduct policy, according to NFL.com's Tom Pelissero.
The league was reportedly unsuccessful in its attempts to reach Ennis. The linebacker's fine stems from his failure to live up to obligations set forth by the NFL following his 2018 offseason suspension for violating the NFL's personal conduct and substances of abuse policies, Pelissero added.
Foster is immediately able to participate in all team activities.