“One call away”

I was listening to Charlie Puth’s “ One call way” and this question came to my mind. I have heard some of you say that in the olders, kids don’t tryout anymore and they get on a team just by calling the coach. I am wondering how does this really work? How does a coach even know your kid? What did you have to do networking wise to prepare for that unexpected phone call. In other words, how do you make these coaches Charlie Puths for you?