French national champion Demare may have won a maiden stage on the Tour – and given his FDJ team their first sprint win on the race since 2006 – but the lingering memory of an otherwise routine stage to Vittel will be the high-speed crash that jeopardised Cavendish’s continuation in the Tour - and Sagan's subsequent disqualification from the race.
Yellow jersey Thomas had already hit the deck in an incident with just over a kilometre remaining when Dimension Data sprinter Cavendish was seemingly forced into the barriers by Slovenia’s Sagan (Bora-Hansgrohe).

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Following Demare’s wheel in a greatly reduced sprint, Sagan had veered across road and then appeared to flick his right elbow towards Cavendish’s face. Cavendish collided into the barriers with his right shoulder and hit the deck at top speed.
Unable to react, Germany’s John Degenkolb (Trek Segafredo) and Britain’s Ben Swift (UAE Team Emirates) both ploughed into Cavendish’s prone body before flying over their handlebars.
Sagan was initially relegated to 115th place, and docked 30 seconds and 80 points in the green jersey competition that he has won for the past five years.
But after a subsequent complaint from Cavendish's Dimension-Data team, the 27-year-old was sensationally disqualified from the Tour by the race jury.

'Cav's gone down!' - Cavendish suffers horrendous crash

Early reports claimed that Cavendish had broken his shoulder, but the 31-year-old could not confirm this after he made a brief appearance – sporting a sling – outside his team bus after the stage.
"Injury-wise I'm going to go and get it checked out," he said. "I will definitely need stitches in this finger, it's bleeding a lot. With the shoulder, it might be something to do with a previous injury, it's sat backwards so I'm not sure if I've done something to the ligament. I'm not a doctor but from the feelings I'm not optimistic."

Cavendish: I'm not a fan of him putting his elbow into me like that

“I get on with Peter well,” a dignified Cavendish added of the role Sagan played in his crash. “If he came across it’s one thing, but the elbow, I’m not a fan of him putting his elbow out like that.
“A crash is a crash but I’d just like to talk to him about the elbow. I don’t know [how bad the injury is]. I’ll have to get it looked at.”

L'arrivée houlouse de la 4e étape à Vittel.

Image credit: Getty Images

For his part, Sagan – who won Stage 3 at Longwy on Monday – had apologised for his actions but claimed he was not at fault.
“I didn’t know Mark was behind me. He’s coming from the right and I wanted to take the wheel of Demare or Kristoff. I didn’t have time to react. It’s not nice to crash like that," he said prior to being disqualified.
With the carnage going on in his wake, Demare had powered clear to pick up a memorable – albeit tainted – victory ahead of Sagan and Norway’s Alexander Kristoff (Katusha-Alpecin). Germany’s Andre Greipel (Lotto-Soudal) and Frenchman Nacer Bouhanni (Cofidis) completed the initial top five – although Frenchman Adrien Petit (Direct Energie) was later promoted to fifth.

Arnaud Demare, vainqueur de la 4e étape

Image credit: Getty Images

Demare, the 2016 Milan-Sanremo winner, took over the lead of the green jersey points classification after Marcel Kittel was caught up in the first crash that split the peloton before the final kilometre.
Kittel, the German Stage 2 winner did not go down in the pile-up which took out most of his Quick-Step Floors train. In the subsequent chaos, Kittel was left in no-man’s land and was unable to fight back to contest the final sprint.

'Greipel was saying Sagan is no longer his friend' - Sergeant

Welshman Thomas was one of a dozen or so riders who came down in the incident, but the Team Sky rider could get back on his bike and finish the stage. He still leads team-mate Chris Froome, the defending champion, by 12 seconds ahead of Wednesday’s Stage 5 in the Vosges mountains.

'I just didn't know that Cavendish was behind me' - Sagan

Prior to the finish line dramatics, the 207.5km stage from Mondorf-les-Bains in Luxembourg was animated only by the solo break of Guillaume van Keirsbulck of Wanty-Groupe Gobert. The Belgian rode more than 190km solo before being caught around 17km from the finish.
Wednesday’s lumpy 160.5km stage from Vittel to La Planche des Belles Filles concludes with the first mountain-top finish of the race – a rendez-vous which is bound to spice up the battle for yellow.