WA Police said the 76-year-old was sitting in the outdoor area of a seafood restaurant on Marine Terrace in Mandurah, 85km south of Perth, when he was allegedly attacked by a stranger around 5.10pm on Wednesday.
The offender allegedly punched the elderly man in the face, causing him to fall back into a flower bed.
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He then allegedly punched the man again while he was on the ground, leaving him with serious facial wounds.
The 76-year-old was taken to Peel Health Campus for treatment.
Acting Detective Senior Sergeant Kris McDonald said police have since arrested and charged a 28-year-old man with aggravated assault occasioning bodily harm.
A local resident said it was distressing to hear of the alleged incident.
“I heard a voice saying just stay away from me, stay away from me,” she told 7NEWS.
“It was really alarming to hear that it was just so random.”
What sparked the alleged incident is still under investigation, but Sgt McDonald said it appeared to be an allegedly unprovoked attack.
The victim was on an “innocent night out with his family” when he was allegedly assaulted in an “unbelievable” act of violence, Sgt McDonald said.
“The elderly gentlemen was simply attending our local restaurant area to meet up with family,” he said.
“Families should feel they can come to the local area here in Mandurah and spend time with their family and go home safely, that’s just unbelievable.”
Police are encouraging anyone with information to contact Crime Stoppers on 1800 333 000 or online at www.crimestopperswa.com.au.
Anyone with dash-cam or mobile phone vision relating to this assault can upload it directly to via this link.