I personally think there are a lot more than 1%. For example, in New Mexico, my previous ward had 8 or 9 girls playing volleyball through middle school. Then, in 9th grade games were to be played on Sunday in our district. Knowing that, only one of those girls even tried out in 9th grade. The same happens here in baseball.
So there certainly are those that will play on Sundays but, in my experience, most Mormons will drop the sport before continuing on Sunday.
It would be interesting to have some church-wide poll. Even a cougarboard poll wouldn't accurately reflect Mormons' views as, I believe, we are more fanatically sports-oriented than most.