The spectator held up a sign as the peloton approached with 45 kilometres remaining and made contact with Tony Martin (Team Jumbo-Visma) on the right-hand side of the road, sparking a massive collision.
With nowhere to go, Martin, who was a part of the peloton in pursuit of breakaway rider Ide Schelling (Team Bora-Hansgrohe), almost brought the whole pack down with him.
Race deputy Pierre-Yves Thouault was far from pleased with the incident and now intends to make the spectator pay for it.
“We are suing this woman who behaved so badly,” Thouault told AFP.
“We are doing this so that the tiny minority of people who do this don’t spoil the show for everyone.”
The spectator’s sign read ‘Allez Opi-Omi’, believed to be a German term of endearment for one’s grandparents - and yet, it was a German whose Tour hopes came to a halt.
“We had everything under control until the crash,” Martin said in a team press release.
“I brought the guys to the front via the right side of the road, but crashed into the sign of the spectator.
“It all happened very quickly; suddenly almost the entire team was on the ground.
“Many spectators behave respectfully, but unfortunately not this one. Fortunately, Primoz (Roglic) came through it well.
“I hope the physical damage to myself and the other guys is manageable.”
The crash was one of two to occur during the opening stage and left Jasha Sutterlin (Team DSM) in hospital, Marc Hirschi (UAE Team Emirates) with a separated shoulder and eight others in need of treatment from the race doctor.
Martin’s teammate Roglic rebounded to finish sixth in the general classification, 18 seconds behind stage winner Julian Alaphilippe of Deceuninck-Quickstep.
According to L’Equipe, French authorities are still searching for the woman who caused the incident.
The Tour de France continues tonight with a 183.5-kilometre stage from Perros-Guirec to the steep finish atop Mur-de-Bretagne. Watch all the action on SBS from 8:30pm (AEST), with live racing commencing at 9:00pm.