An 11-rider move went clear and racing was high-paced in the first 100km as the peloton tried to keep the break within range.
The massive crash then happened just after the 100km mark, with riders from Lotto-Soudal, Deceuninck – Quick-Step, Jumbo-Visma and EF Education First involved.
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Urán, Carthy and CCC Team’s Victor de la Parte abandoned almost immediately.
Roche visited the medical car but stepped off the bike shortly after.
Jumbo-Visma’s Tony Martin also went down but was able to continue, seen leading the bunch with rips in his shorts and some nasty cuts on his rear.
The fall is a disaster for EF Education First, as their chosen man Urán had been riding strong in the opening week and was just 59 seconds down on the race leader.
Roche had a stellar start to the Vuelta, taking over the race lead on stage two and holding it until the first summit of the race on day five, Alto de Javalambre.
Despite losing his slim lead, Roche started stage six in fifth place overall, 57 seconds back on the red jersey.