You've had a lot of responses with great suggestions. The martial arts idea is one of the best. You go to practice with many other new practitioners, no matter what age you start, it's just that kind of sport. You're in a group setting but everyone is so focused on the sensei they are not paying attention to the one guy who can't kick high. Individual teachers will notice if he's having trouble and will help him for a minute, without calling attention to him. I've practiced several kinds and they're all like that. He can practice moves at home in front of a mirror in between classes. Besides the physical aspect, martial arts is all about self-esteem, confidence building, poise, and respect for self and others. Any decent sensei will create a studio where no one would dare make fun of someone else or make someone feel self-conscious.
Second, you mention that he loves animals. If you got him a big dog with lots of energy you could make it his responsibility to walk the dog (unless you live in a dangerous neighborhood, which it doesn't sound like) twice a day. A big dog - especially a puppy or certain breeds - will need to walk far and fast. Kids often don't notice they're exercising because that kind of dog can be fun (obviously as long as he's controllable!).
Third, tennis is another great individual sport, as someone else mentioned. He can start in a beginner class, which often have all ages. Or pony up for some individual classes for a few months until he gets the hang of things. Tennis can be practiced for free against the side of garage or the odd public park, even in fall/spring depending on where Pikesville is? Plus, presently many great tennis players are quite tall - especially Federer. It gives them many advantages; might make your son take interest. Many schools also have tennis teams that you can practice with even if you're not good enough to "make the team."
Fourth, volleyball is a great team sport that does give you lots of exercise but to me (and I have played all these sports), initially requires less coordination and effort than basketball. You also have great advantages if you're tall. Your son might excel at, say, blocking the net, without having to be the best on the court. And FOR SURE, there are no expert 14yo volleyball players - most middle schools are just introducing this sport to kids. Since players rotate around he wouldn't be in the limelight much either.
Fifth, the swimming idea is great. You definitely don't have to be really coordinated, you can start at any level (check your local Y), and it's great all-around exercise. Again with the benefits for tall people, hello Michael Phelps. Again with the situation where no one is looking to see if you're any good - everyone has his face in the water! If you had your own pool or a local membership, it's a fun place to play in the summer - water polo is great for all ages and activity levels.
I agree with other posters about tv. If you assigned him physical chores - especially lawn work, emptying trash cans, and sweeping (that make you walk around the most) - to earn tv watching time, then that might help too.
While I've never heard of these juice pills, which sound good, there are lots of other varieties at Whole Foods or a local health-food store. Plus, if you made a small investment in a juicer you could make your own a lot cheaper. There are recipes online that combine fruits and veggies in a tasty way to maximize nutrition (think Odwalla or Naked beverages).
Last, read these now, then read them again in a few months and they might spark new ideas! Good luck!