I´m not quite sure if this been asked before, but how about a racetrack theme backround?
A bit of paint on the track as a starting grid, and some fences and grass on the side and maybe a grandstand in the backround.
I know there are a lot of Sports out there and if you do one you will probably end up doing them all. But there are soccer, and basketballbackrounds already there, why not one more of the biggest loved sport - motorsport? (Please :-) )