It was posted Friday night on a law enforcement Facebook page.
The incident happened May 7, but is just hitting the internet. There are two concerns: the conduct of the officer and the conduct of the crowd.
The crowd is jeering a DART officer trying to make an arrest in the Rosa Parks train station in the Dallas West End.
DART spokesman Morgan Lyons says the man had been banned from the station, and the officer was trying to arrest him, but the suspect was fighting.
It appears the crowd thinks the officer has the man in a chokehold, but at times, it looks like the officer's arm is also across his chest, not just his neck.
No one moves to help the officer until about 1 minute and 20 seconds into the tape, and that's when things escalate.
About 30 seconds later, a backup officer arrives and things calm down.
Lyons says all law enforcement officers are in challenging situations right now because of mistrust after Ferguson, the Eric Garner chokehold death in New York and the Freddie Gray in-custody death in Baltimore.
He says DART has begun an investigation to review the officer's actions, including the hold he had on the suspect because chokeholds are a violation of DART policy.