Heard about this in a guards mess a few years ago. Has to be played much later in the evening when any 'grown ups' that are left are either too incapacitated to care or are playing. 2 man game. One has a great coat (old fashioned, heavy duty), a helmet and a bicycle. The other has a dismantled shot gun and a couple of shells of bird shot. Referee shouts go, man on bicycle puts on hlemet and great coat and cycles for all he is worth (preferably outside) whilst man with shot gun puts shot gun together, loads it and shoots at departing cyclist!
H&S types do not approve and can imagine headlines/BoA should cyclist not be very quick - anyway - marvellous fun so long as no one is too seriously injured.
Selection for position of cyclist can be through any means deemed appropriate at event (biggest to$$er usually good selection method).