100% Weight gain 100% affects athletic performance. Why you describe is not surprising. I would consider having him do more activities and watch his diet. Our neighbor kid is significantly overweight and is entering 9th grade next fall... he used to be into a lot of sports and seemed to have a positive self attitude towards sporting ability... but now, due to the weight, he is sure he won't play any sports in HS and may decide to limit his participation in them.

I don't think that would be the case if his weight was under control heading into 9th grade.

A lot of boys get pudgy right before puberty and then suddenly shoot up in height. It could be that…

My son's weight gain recently has affected his sport performance. He was 20 to 30 weight percentile, and now he is 80 to 90 weight percentile. He is always an average player. Now, I notice that it is harder for him to do rock climbing, harder for him to run across the field for soccer, harder for him to swim, hike up or down, ride bicycle etc and it seems like he is out of shape. He sweats more, breathe heavily and whine more. It seems like there is no influence on him playing basketball. Is it normal? He is not at puberty stage yet.