Watch: The moment a spectator throws a bike in front of riders at the Giro d'Italia

A spectator has been arrested after throwing a bike in front of riders in the Giro d'Italia 2019.

In a series of events that are yet to be explained, a man is seen walking out into the road as the breakaway riders on stage 18 of the Giro hurtle towards him, then throwing a bike into the middle of road.

The front wheel of the bike comes off as it hits the tarmac, with a quick-thinking spectator on the other side of the road dashing across to clear it out of the way of the oncoming riders and team cars.

Luckily, the three riders in the breakaway Damiano Cima (Nippo-Vini Fantini), Nico Denz (Ag2r La Mondiale) and Mirco Maestri (Bardiani-CSF) spot the road debris early and steer well clear. With the trio spending nearly the whole day out front, and Cima going on to survive by the skin of his teeth and take the stage win, it would have been cruel for their efforts to have been ruined in this manner.

EF Education First rider, Sacha Modolo, posted a video showing another angle of the incident on Twitter, capturing the moment the man calmly walks out before hurling the bike to the floor after the race commissaire's car has passed.

The Italian cyclist then confirmed the man had been arrested by police following the incident.

At present, the motivation behind the man's actions are not known. Was it some sort of protest? With Grand Tours no stranger to demonstrations, after stage 16 of the Tour de France was neutralised following pepper spray being used on protesters by police and being blown back into the riders' faces.

Or maybe he just loves bunch sprints and could sense the breakaway were going to go the distance? We'll bring you updates when we have them.