What is a stage flat?

A stage is one part of a race that's divided into several stages, or days of racing. A flat is a flat tire, a puncture. If a rider gets a flat he has to stop riding until his support car catches up with him and provides him with a new wheel or a new bike, after which he has to ride hard to catch up with the rest of the races. This usually spoils the rider's chance of winning that stage, but might still allow him to win the overall race. At amateur level the rider might have to fix his own flat along the roadside. A star rider might call for one of his team members to trade bikes with him, allowing the star rider to continue while leaving the support rider to wait for the support canr.