Stanford coach Jim Harbaugh, a former NFL QB who played for his dad in high school, likes having players, such as his NCAA-leading running back Toby Gerhart, whose fathers were their high school coaches:
“Kids who have been coached by their fathers, they are almost always really coachable kids,” Harbaugh said. “They take advice, they’re willing to learn. I’m happy to have them.”
Any teenager who will listen to his father will listen to any adult male authority figure.
So, is the correlation between star athletes and fathers who are employed coaching them in high school nurture? That makes sense. Football is a complicated game, and having a professional coach around the house can certainly help.
Or, is it nature? That also makes sense. Coaches tend to have been very good players, so some of their skill is likely passed down.
Yet, keep in mind a third possibility: reverse nepotism. There are a few high school coaches who have inherited their jobs from their star sons. Generally speaking, high schools aren't supposed to recruit grade school athletes, but hiring a kid's dad as a coach is okay.
(There's also regular nepotism, too, such as the high school coach who had his son play quarterback and Ben Roethlisberger, now QB of the Super Bowl champ Steelers, play wide receiver so his son would have a large target to throw the ball in the general direction of. The son went to a Division 3 college, washed out as quarterback, but wound up making a good Div 3 wide receiver.)