Joe joined him and while the alleged tagger was initially apologetic, he suddenly began throwing punches, Geensma said.
"I got a left hook in the jaw, a right hook in the eye and a bunch in the ribs. Then he [Joe] put his hands up and said 'take it easy' and the man gave him such a hard left hook that he left the ground and his blood splattered over me.
"Describing it as vicious is an understatement."
Joe was left lying on the ground, conscious but barely able to walk as others helped him to Shorecare Urgent Care Northcross across the road, where an ambulance was called, Geensma said.
A St John spokesman said a man was taken from Shore Care to North Shore Hospital in moderate condition around the time of the incident, but could not confirm if it was Joe.
Geensma said his partner, Catherine Hollway, posted photos on Facebook that she alleged were of the man involved which were then shared on North Shore community Facebook pages.
Hollway had been told by a Farmer Joe's staff member Joe needed surgery following the incident.
Joe was "a gentle, beautiful man", Geensma said.
"I just feel really awkward about suggesting we go down [to confront the alleged tagger]. That's not the outcome that was wanted at all."
As Joe was being helped, others rushed to the scene, some chasing the alleged attacker and two men with him.
The man had jumped on the back of a moped and told the rider - who was not known to him - to take him away, but bystanders pulled him off, Geensma said.
"[The three men] then took off down East Coast Rd."
A police spokeswoman said they were investigating the assault and were pursuing strong lines of inquiry.
If you saw the incident or have any information that can help police identify men contact North Shore Police on (09) 477 5000. Alternatively, information can also be provided anonymously to Crimestoppers on 0800 555 111.