The spectators thought they were safe perched on their wooden-pallet-style stand in the town of Serra north of Valencia.
But slowed-down TV images showed the animal attacking the bottom of the upright support as it chased a bare-chested reveller through the streets – toppling the ten people on top.
Two people were rushed to hospital after several fell backwards from a height of around six feet and smashed onto the hard ground.
They included a Valencia-based police commissioner who was on holiday in the area and suffered a head injury and broken arm that kept him in hospital overnight.
The spectators that managed to remain on top of their makeshift stand for a few seconds longer – including two that appeared to be teenagers – toppled forwards near the bull which fortunately for them carried on running forwards instead of turning back and goring them.
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As well as the two people taken to hospital, four other casualties suffering light injuries were treated in a field hospital set up in the town library.
The event was suspended after the scare.
Earlier this month, two men escaped serious injury after being tossed into the air in separate incidents at an annual bull festival in the Spanish holiday resort of Calpe near Benidorm.
Dozens of people are injured every year at annual summer festivals involving bulls in Spain.
In the Valencia region including the provinces of Castellon, Valencia and Alicante they are known as Bous Al Carrer which literally means Bulls on the Street.
In 2015 more than a dozen people died at bull festivals across Spain.
Three events in different parts of Castellon on Sunday left four people injured, including a man who was gored in the arm and suffered a broken rib in the town of Nules.