The bike is an S1 or S2 model, also known as the 3-1/2hp or 6hp Sports. The distinctive front brake is a give-away. Probably the smaller 3-1/2hp Sport. Made 1921-23, this one is 1922-23 model, judging by the type of inlet manifold.
Some sort of Gymkhana, with the riders participating in a version of 'tip the bucket'.
-Doug