My 20 year old son always had trouble with sports -- baseball, volleyball, football, etc. After years of practice, even though he wasn't good when he began at age 8, by the age of 13 he developed real skill with soccer, and was quite good at snowboarding. Go figure!
My 10 year old son has been much the same -- not good at any sports -- but, he is great at DDR! He's actually quite graceful as far as dancing goes. I actually think that he could be fairly good at sports, but he doesn't have the desire or the self-confidence required.