Protesters blocked the road 30 kilometres into the 218-kilometres stage to Bagnères-de-Luchon. Near the town of Fanjeaux, farmers upset with recent EU funding cuts threw hay bails on the road. Police used pepper spray to disperse them, but the gas also reached race leader Geraint Thomas (Sky) and others in the group.
"When I woke up this morning I didn't expect to get hit by pepper spray," said Daniel Martin (UAE-Team Emirates).
"Luckily I was further back. I definitely felt it on my face and forehand, breathed in a little bit of it. Some of the riders were worse off. The team medical staff did a great job of giving the riders attention quickly. The race dealt with it the best they could. All these new experiences, but that's not one I expected to get this morning when I woke up!"
"It was certainly unfortunate that it was still lingering around when we came through," Thomas explained. "I could feel it in my eyes, a little bit of tingling. I gave them a wash and rinsed my mouth out. I was kind of lucky it didn't affect me too much."
The race was stopped for over 15 minutes so police could deal with the block caused by farmers from the local Ariege department. Doctors and staff quickly began to help their riders when complaints came through their two-way radios.
"It was burning straight away and they said, 'We've got this gas burning. We need to stop. It's not possible to ride…' and stuff like this," Team Sky sports director Nicolas Portal said.
"It was irritating me quite a lot in the car, so for the riders it was pretty strong."
"I am just glad that everyone is all right – the riders and farmers and police, I think everyone has come out all right from it," Team Sky's Chris Froome said.
"I just sprayed some water in the eyes and water in the face. My throat, nose and eyes were burning afterwards, but I think quite a lot of riders were in a similar situation, so I think we were all grateful for the temporary neutralisation just to have a couple of kilometres to clear our eyes, nose and throat out and then the race continued again.
"Thankfully, the effects didn't last long but temporarily everything was stinging and burning but it wore off pretty quickly."
The race went on. Adam Yates (Mitchelton-Scott) attacked free on the final Col du Portillon climb, but crashed on the descent. Frenchman Julian Alaphilippe (Quick-Step Floors) passed him and won the stage.
The incident comes amid heightened awareness due to recent terrorism problems around France and the world and also follows problems with unruly spectators on the road in the previous stages.
"I think it's hard [to prevent] when it's just on the open roads, it's not a closed stadium so it's a lot harder," Thomas added.
"The police and [organiser] ASO are doing the best they can I suppose. We don't feel unsafe, it's just unfortunate sometimes but I think everyone is doing the best they can. Hopefully everyone can just behave."
"Tensions are high due to a lot of things, there's always that threat of terrorism at sporting events around the world and for the general public, so of course tensions are high," Mitchelton-Scott sports director Matt White said.
"I've never seen a protest in the last 20 years that stopped a race like this, especially one of this high quality. I saw some riders sputtering and coughing in other teams, red eyes, doctors washing eyes and faces. It was a scene I'll never forget for sure."
"A cyclist's job is dangerous as it is," said race director Christian Prudhomme at the finish in Bagnères-de-Luchon. "We shouldn't be adding extra dangers to their job. They take enough risks already. I insist. We have to let them pass unhindered."
The incident is developing still, but officials from the local Aude Prefecture reportedly have begun an investigation into the farmers' protest.
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Gregor Brown is an experienced cycling journalist, based in Florence, Italy. He has covered races all over the world for over a decade - following the Giro, Tour de France, and every major race since 2006. His love of cycling began with freestyle and BMX, before the 1998 Tour de France led him to a deep appreciation of the road racing season.
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