The cycling world is baffled by why the fastest Tour de France rider's chain falls off as he celebrates over finish line

• Mark Cavendish, the fastest rider at the Tour de France, has won two stages at this year's race.
• But when the "Manx Missile" celebrates as he crosses the finish line, his chain sometimes falls off.
• It's unclear why, but it appears a violent jerking motion causes the chain to slack and pop off.

Mark Cavendish, the fastest rider at the Tour de France, has returned to the great race in style, winning two stages so far, for a career total of 32 Tour stage wins. But something weird happened on stage six on Thursday as he posted up to celebrate across the finish line: His chain fell off.

-daniel mcmahon (@cyclingreporter) July 1, 2021

Here's a close-up:

Many expressed surprise and confusion about what was going on. As folks on cycling Twitter speculated, it's likely several things happening at once.

One, as the fastest sprinter, he's putting massive power into his pedals and charging to the line extremely quickly (in this sprint, he hit 43.5 mph). So there's lots of forward momentum.

-daniel mcmahon (@cyclingreporter) July 1, 2021

Second, as he sits up to celebrate, he stops pedaling abruptly and even backpedals a half stroke, which causes a violent jerking motion on his drivetrain.

His rear-wheel free hub spins backward, causing the chain to slack and drop off the chain ring.

(The road surface at the finish appeared to be smooth on Thursday, so it's unlikely there was a bump that caused the chain drop.)

"There must be some backpedaling happening while there's reduced tension on the derailleur cage," experienced US racer and cycling coach Adam Myerson suggested.

And it's not the first time the Isle of Man rider has lost his chain, as this clip from a race in April shows:

-Owen Rogers (@OwenRogers) April 12, 2021

It doesn't appear to be a safety concern since Cav is sitting up to celebrate and doesn't need to keep going. But it's still kind of weird to see him drop his chain. After all, the bikes at the Tour de France cost more than $10,000, and you'd expect all the equipment to work flawlessly.

Meanwhile, Cav is closing on Eddy Merckx's record of 34 Tour stage wins.