While monitoring an event on Canvey Island, Essex, UK, officers received an alert about a motorbike driving recklessly.
So they immediately changed course to pursue the motorbike, with a police helicopter overhead. They stopped the biker at an estate in Basildon.
However, as they tried to arrest the rider, a crowd of up to 30 people surrounded them.
Then, a woman threatened the officers with a hammer before a man doused them with petrol.
The crowd then yelled:
"Who's got matches, who's got a lighter? Let's set them on fire!"
The officers then began to panic as some of the onlookers were smoking. The officers also had tasers, which could have triggered sparks and set fire to petrol.
As many as 90 officers rushed to help prevent their colleagues from being lit on fire. Two of the officers had to be rushed to a hospital as they ingested the fuel.
The officers then arrested and charged several people from the group, including Justin Jackson, 28, who threw the petrol.
Jackson is now facing a three years and nine months prison sentence.
Reliving the ordeal in BBC's Critical Incident documentary, one of the officers at the incident, PC Andrew Bird, said:
"As I was trying to control a gentleman who had run out of the middle of nowhere, this other chap has appeared with a watering can."
His colleague, PC Matthew Cutts, then stepped in to fend off the new attacker.
"I could smell petrol. So I sort of fumbled around to get my baton out, but once I've got it out, I've put it behind my head and just struck him in line with my training."
"It's not a random act of violence. It's a controlled measure that we are taught to use to get people away from us."
PC Cutts, who was unaware of the content of the watering can, then started feeling stinging and tingling on his skin.
Speaking out about the terrifying experience, Chief Inspector Jonathan Baldwin said:
"I was hearing them shout 'light them up.'"
"I don't know how we didn't just cut and run. But then that's not the way [cops] are. We all stuck together."
"There's something running in the core of us that says you don't run away from the danger. You run towards it."
The inspector added:
"One match, one lighter, one spark could result in us going up in flames."