The 50mm just won't focus fast enough for fast moving objects even on a 1D series camera, put it on an XT series and the speed drops considerably. Prefocus and you'd be OK. A flash would get rid of the shadows but you'd need at least a 580EX flash to get the range youd need for these types of shots. A 70-200 and a flash would work well here. The built in flash is pretty much worthless though.

JS