Authorities in Northern California are investigating an altercation between a police officer and a man in a wheelchair that was captured on video and circulated online.

A San Francisco police officer is seen in the video apparently trying to push the man and his wheelchair off the curb of a sidewalk. The wheelchair almost tips over, but it remained upright and a seat belt kept the man in his chair. The officer can be heard complaining on the video that the wheelchair ran over his foot.

The incident occurred Sunday afternoon while police were responding to a disturbance. Four men were issued citations.

A police spokesman declined to identify the officer involved and says the department is investigating the incident.