The 70-year-old victim was taken to hospital after the incident in Bankwood Lane, New Rossington, at about 7am this morning.
He was stood in the street with a group of residents during an organised protest against a nearby recycling centre, which they claim is causing an infestation of flies in the town.
During the protest a man on a quadbike rode past and fired at the crowd with a paintball gun causing injuries to the man's face.
Unconfirmed reports suggested the paintball had gone into the man's eye.
Detectives are now investigating the incident.
A South Yorkshire Police spokesperson said: "It is reported that a man riding a quad bike fired a paintball gun at an elderly man, causing an injury to his face.
"A 70-year-old man has been taken to hospital, however his injuries are not thought to be serious.
"The incident happened during a planned protest at the nearby recycling centre.
"The rider of the quad bike is said to have had his face covered and officers are asking anyone who saw what happened to call 101 quoting incident number 158 of 25 July 2017."
Residents told a recent planing committee meeting at Doncaster Council that people were becoming ill over the number of flies being attracted to the nearby Morris Metals site.
Council planning officer Dave Richards told the committee that in May the site had been issued with an enforcement notice from the Environment Agency because of the number of flies at the site. It had raised concerns over the height of stockpiled metal, and the arrival of metal containing flies.
Mr Richards said the firm blamed a machinery break-down.
A re-inspection on June 8 stated that the firm had sorted the problems, but the EA pledged to continue to monitor the site.
To resident's dismay, the company was granted planning permission to extend the site at the meeting.
The Environment Agency, Doncaster Council and the company have been contacted for comment.