Selection Bias and Football Parents

From MMQB:

"It surprises me that parents—and 23 of those we interviewed who spoke this way, nearly a quarter—cede the decision to play or not play high school football to their sons. That has changed in the time since I was a (quite marginal) high-school athlete in Enfield, Conn. If my father and mother thought the sport I was playing was excessively dangerous, they’d have interceded and recommended and/or demanded I not play. But many of the parents we interviewed in 49 states said it was up to their son where he would play. I understand wanting to empower your children, but I’m not sure empowering 15- and 16-year-olds who make decisions based very often on emotion is a smart call"

Except this is from interviews with parents of sons who are playing high-school football.  The parents who tell their kids they can't play football are not going to be in the sample.