I don't have a problem with anyone in this thread, but I do have a problem with some of the attitudes. There are folks intimately knowledgeable on the subject, there are folks that admittedly do not know about sports at this level, and there's folks on both sides who are dismissive of others with a different viewpoint.
I do know just a tiny bit about coaching non-school-related (and school-related) sports, both recreational and competitive, having coached both, and coached extracurricular sports at both recreational and competitive levels. I also know about multiple-sport athletes, having raised one myself.
There's a lot of people getting hot about whether this kid was right or wrong, and he was wrong.
There's a lot of people getting hot about whether this coach was right or wrong, and he was wrong.
When someone signs up for a sport, they are making a commitment to the team. Choosing at some later point to not honor that commitment is the same as choosing not to honor any other commitment. Indeed, that's what youth sports is all about, and why participants do so much better later in life than nonparticipants; because they have learned about making and honoring commitments.
When someone coaches a sport, they are making a commitment to the team. Failing to make team rules known to the athletes before they agree to participate is choosing to not honor that commitment, because the coach is responsible for providing the structure in practices and games, and the framework around which the team operates.
As has already been pointed out, lack of effective communication from both sides is what caused the whole problem.
As far as using sports as an entry to college; many are correct, very few kids get a "full ride" scholarship for any sport. That said, college acceptance is not anything like it used to be, and not having many full scholarships available doesn't mean that sports are not one of the critical experiences to getting into a good college.
Good grades don't guarantee anyone a place at a 4 year college any more. A student can be 4.0+ GPA and Honor Roll student every single year of middle and high school, and all they're guaranteed of is a place at a community college, paying every dime of their way.
Nowadays, the good institutions look at the whole package:
Was the applicant involved in sports?
Was the applicant involved in the music program?
Was the applicant involved in school government?
Was the applicant a tutor or student aide?
Was the applicant involved in their community? If so, what extracurricular activities and/or programs were they involved in?
The 4 year universities are looking for the best of the best, because they want to be known for producing the future leaders of business and government. This allows them to compete for the best student body possible and ensures that their reputation is the best it can be, because higher education is even more competitive now than it has been in the past.