The Scandinavian Touch Walkstool was made with sports photographers in mind as well as any photographer who needs to sit on the job.
Built with 3 telescoping legs, the Walkstool is light enough to attach to the photographer's belt for travel but sturdy enough to support the largest of photographers (a company presentation shows a sedan perched on 4 Walkstools).
It's available in 3 sitting heights - 45cm, 55cm and 65cm - and 2 different seat sizes (L, XXL) for different-sized bodies. The 45cm, 55cm and 65cm Walkstools are available now with the size L seat; the XXL seat version will be available only in limited quantities until later this year.
A list of international distributors is on the Scandinavian Touch website.

Walkstool 45cm, 55cm and 65cm models

A Walkstool collapsed and attached to a photographer's belt