Does he have friends you can get to come over and do things with him outside? Friends whose parents you know well enough to suggest that you all enroll the boys together in some activity? I would not try forcing him onto a sports team if he is really not into that, but have you ever looked into sports such as golf, archery, fencing or tennis, which are either individual or just require one other person? He might find them interesting and he might associate the word "sports" with just soccer or baseball and hate the idea. You could offer to let him choose something to enroll in, while emphasizing that he does not have to play any team sport (unless he somehow suddenly takes an interest).
It's hard to do iin winter, but can you take him away on a weekend and make it fun (with some movies and other stuff thrown in) but a lot of hiking? Maybe even some cross-country skiing since you're in NY? If you approach it as "we're having a mini-vacation" instead of "you have to get outside and move" it may sneak up on him that he actually likes the skiing and wants to keep doing it.
And yes, don't let him watch TV or play games etc. until he earns it with exercise. If you have issues with the winter weather, get an exercise bike or treadmill for indoors but be sure he actually uses it.