Authorities are investigating a violent assault on a Metro train after a rider captured the incident on video.

The video, which an unidentified rider captured and sent to NBC4, depicts two riders getting into an oral argument before one of them begins aggressively elbowing the other in the face. The incident occurred on Friday night on the Orange Line between the Clarendon and East Falls Church Metro stations.

The witness who sent in the video told NBC4 that the alleged assaulter was much older than the victim and the two may have been related. “Apparently the son said something that the father thought was disrespectful,” the witness said. “And then you can see on the video what ensued. It was really pretty shocking.”

Metro spokesman Dan Stessel tells DCist that the Metro Transit Police were not contacted the night of the incident, but the man who shot the video sent it to their detectives yesterday. They have opened the case and the investigation is ongoing, he says.