An 84-year-old woman has suffered serious injuries in an alleged "unprovoked" assault in Adelaide's southern suburbs, police say.
Police alleged the elderly woman was punched at the intersection of Thomas Street and Marion Road in South Plympton about 3:50pm on Monday.
"It appears this was an unprovoked and isolated incident with investigations continuing," police said in a statement.
Police said members of the public helped the woman after the alleged attack before she was taken to hospital with serious injuries.
"Police would like to thank members of the public who went to the victim's aid immediately after the incident and assisted police in the apprehension of the suspect," they said.
A 31-year-old Edwardstown man was arrested and charged with aggravated assault causing harm.
The man was refused bail and has remained in hospital to receive treatment, police said.
He is expected to appear in court at a date to be confirmed.
Detectives ask any witnesses or anyone who has CCTV, dashcam, or mobile phone footage to contact Crime Stoppers.