This whole thread reaks of helicopter parenting. Sports are supposed to be fun. If a kid enjoys playing other sports then they should play other sports. If they have more fun just playing one sport than that is
what they should do. Unless it is affecting their schoolwork it really shouldn't be a parent's decision to make. If your DD cannot play for TB team A because she plays another sport which she enjoys playing
then find another team which will allow her to play that sport.
Partying, drinking, drugs, and sex, I am sure most HS kids find some of these FUN too. Why in the name of fun don't you let your kid do them? Because you as an adult understand there are consequences to the decisions they make and they are not fully aware of what those consequences can be. If a player wants to play in college, then the parent may actually have to step in and say this is not a good choice for you because it isn't the best path for you to achieve your goal. No if you just want to keep playing rec ball or some form of high level C ball, then by all means, hook that athlete up with 4 or 5 sports as long as she is having fun. Beats the alternative of partying, drugs, drinking, and sex.
BTW, has anyone told weightlifters/powerlifters they shouldn't train their bodies year round? What about fitness (cardio) trainers?