track sounds like the obvious choice. tall, skinny, not too coordinated, with fast legs..........screams runner to me. Depending on his endurance he could do distance or sprints, or both. long arms could also help with slinging objects like the discus or hammer throw, although they both require strength too.
Track would probably be best for him. If he would start working out though, he'd do better in every sport.
I agree with track. Tall and skinny usually means a good runner. Maybe even cross-country =) Bball could be a possibility, but with the lack of coordination, it could be ugly
Tall and skinny does not mean a good runner. A good runner has to have a good core, he/she has to workout and achieve a good core. No matter what the sport, if he is going to be successful he will have to work out.
Definitely tennis or track. Not many people believe it, but basketball is actually a physical/tough sport, too skinny, and you'll just get pushed around