Multiple news media outlets reported that the woman was in custody on Wednesday. The woman, 30, turned herself in, Colonel Nicolas Duvinage of the Landernau, France, police told France Bleu Finistère.
Video from the race on Saturday showed the woman leaning into the road while holding up a cardboard sign for the television cameras. Because she had her back to the approaching riders, she failed to realize how close the riders were to her position and did not pull the sign out of the way of the racers in time.
The German rider Tony Martin, who was near the front of the pack of cyclists, crashed into it with his handlebars and, losing his momentum and his balance, fell onto the road in front of the tightly packed field. That set off a cascade of collisions that led to several injuries; dozens of riders were involved in the crash.
The crash happened during the first of the race’s 21 stages, in the municipality of St.-Cadou. The sign read, “Allez opi-omi!” — a mix of French and German that roughly translates as “Go, granddad-grandma.” The police said that the woman holding it, who was wearing glasses and a yellow jacket, left the scene before investigators arrived.
The specific details of how she was identified or arrested were unclear on Wednesday. The police in France did not respond to several requests for comment.
Pierre-Yves Thouault, the deputy director of cycling with the Amaury Sport Organization, which runs the Tour de France, had threatened to sue the fan. “We are doing this so that the tiny minority of people who do this don’t spoil the show for everyone,” he said.
But on Thursday the race’s director, Christian Prudhomme, told Agence France-Presse that race officials had withdrawn their legal complaint against the woman. “The incident has been blown out of all proportion,” Prudhomme said, according to A.F.P. “So we’d like to calm things down now that the message has got across that the roadside fans need to be careful.”
Since it takes place on public roads in France, the cycling race gives millions of spectators a chance for up-close views of the action year after year. But fans have often been overzealous in encroaching upon the race, and have at times interfered in the competition by running alongside the riders or blocking their path.
Fans posing for selfies with their backs to the field have become a particular issue in recent years, and race and team officials — and even riders — did little to hide their anger about Saturday’s crash.
There have been numerous incidents over the years in which competitors and fans have become entangled, though mass pileups caused by spectators like the one on Saturday have been less common.
On Instagram, Martin wrote: “To all the people next to the road who think that the Tour de France is a circus, to people who risk everything for a selfie with a 50 km/h fast peloton, to people who think it’s nice to show their naked butt, to drunken people who push us sideways on the climbs, to people who think that it is a good idea to hold a sign into the road while the peloton is passing. I want to ask this people forcefully: Please respect the riders and the Tour de France!”
“Fans, please stay off the roads,” tweeted Richard Plugge, the general manager of Martin’s team, Jumbo-Visma. “And if you want to pay attention to your opi and omi, visit them.”
Jacey Fortin and Aurelien Breeden contributed reporting.