If you force your child to do a sport, he will resent you for it and not continue it later in life as it was always something my mum/dad wanted me to do.
If you want to get your child involved in something meaningful, they have to see it as a fun thing to be doing. They need to feel a part of it. At first it will be very daunting for a child to enter a room full of other children they don't necessarily know and to do an activity they cannot do yet.
I'd be asking questions why doesn't he want to get involved. No child wants to miss out on something fun.
Is your child an introvert and so may need gentle guidance and persuasion to see the fun in being a part of a martial arts club or whatever sport.
Is your child lazy? Is this due to an insufficient intakeunhealthy, or un-balanced diet? Here is just one site of many on the right vitamins? Diet affects everythinginternet that can guide you in providing a healthier diet if that is what is needed.
If you want your child to play football, do YOU play football with him to get him interested?
I train in a martial art and I have no intention of forcing it on my daughter, what I am doing however is getting her interested in it indirectly, by showing her how much fun it can be and how easy it is for me to do things when she is trying to stop me etc. Through this "play" I am creating an interest in something that I am hoping she will want to be a part of, or at worst, she finds interest in another martial art! Who knows. Kids need guidance, not to be forced into anything.
I hope this helps