He was taken to hospital with injuries to his mouth and ears, but discharged later that day.
The assault only stopped when a member of the public pinned the attacker to the ground. A man has now been arrested in connection with the incident.
Chris, 45, who lives in nearby Wellington Road, said: “I went in during the afternoon, and there was this bloke having a go at the security officers.
“He was giving out loads of abuse. He grabbed one of the officer’s clipboards.”
Suddenly, the man “lunged over the counter” and grabbed the victim by the throat, Chris said.
“He dragged him over the counter,” he said.
“The officer was up against a glass window and this bloke was punching him in the face.”
Shoppers visiting the store during the afternoon stood “open-mouthed” as the assault happened.
“There were at least 100 people there watching it,” Chris said.
“A random man came forward, pulled the attacker off the security officer and pinned him down.”
A spokesperson from Dorset Police said officers were called shortly before 3.45pm.
A 28-year-old man from Poole has been arrested on suspicion of assault and possession of cannabis and is currently assisting officers with enquiries.
Shoppers at Asda yesterday spoke of their shock.
Allan Penhale, who lives in Bournemouth, said: “Any kind of violence is appalling and shouldn’t happen.
“I shop here often and all the staff are so nice and helpful, which makes this so disappointing to hear.”
Dennis Tompkins, also from Bournemouth, said: “It is just unacceptable but unfortunately it’s the world we live in now.
“There are too many people doing what they like, getting up to no good and getting away with it.”
"I also witnessed the end and Im almost sure I heard a tall blond manager whos name badge said Shaun telling a young worker in a black shirt dont get involved I agree with X, managers clearly dont care about their staff at least 5 of them were stood well away watching and would prefer the public deal with it. Cowards all of them and respect the the public and the security officer (who was clearly badly injured and covered in blood) who risked their own safety to protect others true heroes"
"I was walking in the store when this started and I saw the man and the security guard (with blood pouring down his face) bravely take down and hold that thug on the floor, while all the managers stood hopelessly watching him being battered!!! It comes to something when the public have to step in to save a member of staff from a beating of a lifetime"

source: http://www.bournemouthecho.co.uk/news/15924460.Security_officer_at_Asda_attacked_by_man_who_punched_him_repeatedly_in_the_face_in_front_of_horrified_shoppers/?action=success#comments-anchor