Within 20 metres, media official Chema Rodriguez stepped into the path of the French stage winner. He crashed along with second place Dutchman Dylan van Baarle (Sky) and Belgian Dylan Teuns (BMC Racing), who placed fourth, landed against the barriers.
"It was crazy to have that risk at all when somebody went across the line," said Geniez, who won from an escape.
"I went down first, luckily a cop held me up. Despite all the measures for safety, despite the security, I don't understand so many people are in the finish area. What would have happened if 100 riders were finishing in the lead group. You could not stop it."
Rodriguez's job is to help organise the photographers at the finish line. In the narrow finish area, confusion reigned when workers reportedly heard more Vuelta official cars were driving through.
Van Baarle was worse off but did not speak after the finish. He should be able to race ahead in stage 13.
"I just saw the video," Team Sky sports director Gabriel Rasch said. "I saw the person running with their back to the riders and I saw the riders crash into him. He's a person that shouldn't be there.
"At a place like this, you should look at the riders. It's their safety that is the most important thing.
"I just heard from the doctors so far that it doesn't look like anything is broken. He's just in pain with some bruises. We'll see during the night how it is. Hopefully he can start tomorrow."
Sky later confirmed that Van Baarle had suffered minor injuries, though was suffering pain in his leg.
“He has a few cuts to his right hip and elbow as well as a bruise on the right side of his ribs.
“He has quite a lot of pain in his right thigh - at the minute I think this is just from the impact of the bike on his thigh but we will need to see over the next few hours."
Today, Van Baarle formed part of the large escape of 18 cyclists. Jesús Herrada (Cofidis) earned enough time to take the leader's red jersey from Simon Yates (Mitchelton-Scott). Dylan Teuns also made the move and saw the crash.
"I saw someone from the organisation running in front of Geniez, who then crashed right into him as did Van Baarle," Teuns said.
"I was also somewhere in there when the crash happened but I didn't actually go down and I was able to push myself towards the barrier."
The riders association president, Gianni Bugno, issued a quick message to the Vuelta a España organiser after the incident along the Costa Verde.
"It is not acceptable that after months of work of all the stakeholders to improve the safety at the races, we are still seeing episodes such as the fall of the today's Vuelta," said Bugno.
"I am really tired of seeing this superficiality in applying the regulations set out in the Organiser Specifications. This lack of attention from the organisers demonstrates a total lack of respect towards us that have worked hard to improve the safety at the races and a total lack of consideration towards the riders."
Rodriguez appeared with a large bandage on his forehead, but continued with his work in the pressroom after stage 12.
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