Tour de France director Christian Prudhomme has called for calm after a number of incidents tarnished the 12th stage up to the iconic Alpe d'Huez on Thursday.
Italian Vincenzo Nibali sustained a fractured vertebra when he crashed about four kilometres from the top of the 13.8-km climb after being hit by what appeared to be either a spectator or a police motorbike.
The 2014 champion believed he may have touched a motorbike but television footage suggests he came into contact with a spectator on the right side of a narrow road that lacked barriers to protect the riders.
Defending champion Chris Froome, who has often been subjected to negative treatment from Tour de France fans, was booed all the way up to the summit and one spectator ran alongside the Briton before slapping him on the shoulder.
"I'm calling for serenity," Prudhomme told French radio station France Info on Friday before the start of the 13th stage, a 169.5km ride from Bourg d'Oisans to Valence.
"It's the organisers' responsibility to protect the riders," said Froome.
The four-times champion's Sky team mate Geraint Thomas, who extended his overall lead with a stage victory, was also jeered at the podium ceremony, while Frenchman Romain Bardet narrowly avoided a collision with a fan lying on the road.
Sky are unpopular with parts of the cycling community in France, where their domination -- winning five of the last six Tours -- is reminiscent to that of disgraced Lance Armstrong's U.S. Postal team in the early 2000s.
Froome has often had to fend off doping allegations since he won his first Tour in 2013. He was cleared of an offence days before the start of this year's race after he was found to have excessive levels of asthma drug salbutamol during one stage at last year's Vuelta a Espana.
He was booed again at the start of the 13th stage, although there were cheers for Thomas when they went to the podium to sign the start sheet. Both were jeered when they cycled back to their team bus.
"I firmly condemn these incidents," added Prudhomme, who insisted that most of cycling fans were non-violent.
"Then we know it's always a bit special at Alpe d'Huez or on the Mont Ventoux. I want the fans to respect the riders. In cycling, you can support a rider without booing the others."
