I used to play wing half as it was called in those days.
And you may not believe me but I used to love going to practice after work on my own many times and used to practice throw ins and measure how far I could throw the ball and the next time try and throw it further and then further still etc etc. Its not rocket science is it? How many times do you see a proper movement of the spine and upper body to be able to throw it further? How many times do you see a run up and throw to generate more distance?
No, I never did get to read any coaching manual!
I tend to think it was probably Dario's idea that young kids should not be using body leverage in case they injured themselves.