A 72-year--old Labour supporter was attacked and hospitalised with a suspected broken jaw while out canvassing in Rotherham.
The man, who has a walking stick, was assaulted while door knocking a property in Parkstone Crescent, Hellaby at around 4pm on Sunday.
A 51-year-old man was arrested on suspicion of causing grievous bodily harm.
The attack has caused anger from political candidates in the South Yorkshire town.
Sarah Grant, chair of Rotherham constituency Labour Party, tweeted on Sunday evening: “My 72 year old comrade, who has a walking stick, was assaulted today door knocking in Hellaby in the Rother Valley constituency.
“He is currently at Rotherham District General Hospital undergoing treatment for facial injuries.”
Sophie Wilson, Labour's Prospective Parliamentary Candidate for Rother Valley said: “As many may have already heard, I am sad to report that one of our members, Bob, was assaulted while out campaigning. This was a completely unacceptable and vicious act which has been reported to the police. Because this is now being investigated it would be inappropriate of me to comment further on the incident.
“I have visited him in A&E and although hurt, he is doing well and is in good spirits. He will not let this get him down. We could all learn a thing or two from Bob - who is a 72 year old campaigner fighting hard for his community with respect and passion. My thoughts are with him tonight and I wish him a speedy recovery."
South Yorkshire Police confirmed an investigation into the alleged attack is taking place after a man in his seventies was injured.
A police spokeswoman said: “We received a call at 4.06pm on Sunday, 24 November.
“The caller reported that a 70-year-old man had been assaulted by a known man on Parkstone Crescent in Hellaby, Rotherham.
“The 70 year-old man has been taken to hospital with a suspected broken jaw.
“A 51-year-old man has been arrested on suspicion of causing grievous bodily harm.
“He remains in police custody.”