The football player comparison is a bad anology. The fact is many kids, even athletes, have congenital a cardiac arrhythmia or other problems that, combined with obesity and many of those strenuous activities, could cause trouble or death. Look at how many outwardly "normal" kids drop dead doing sports. The vast majority had passed the required pre-athletics physical.
incidentally being overweight doesn't make you un-healthy.
I'm overweights. yet. I don't have cholesterol, high or low blood pressure or any other condition(other than my non related Asthma from childhood). meanwhile a lot of thin/fit people are high cholesterol and blood pressure issues or other issues. Weight itself doesn't necessarily have any relation to health issues, though I'm not talking about the needs to bus seats type of fat here, which is getting very common over there.