I highly recommend Jefferson Deadlifts.
Bill Starr recommended rotations with a barbell on your shoulders
I recommend throwing discus, and I am not in any way biased about this.
Honestly, when I played soccer for the first time in years, I got sore in certain muscles at each side of my body and couldn't figure out why at first. I then tried various movements and noticed that rotating my legs, hips and back contracted a lot of the sore muscles.
Even though I somewhat buy the argument that strength is general, I do think something is getting left out if you only do the SS lifts and their assistance lifts, not that I have any clue whether you should add more and if so what you should add.
Rotation work does seem to me to hit muscles you normally don't hit much with normal barbell movements.
I started on the SS wagon to improve my swing speed in golf. It worked to some degree. It helped even more for just general endurance throughout a round.
I had always tried to do the trendy sports specific training, and it never worked. I am now a firm believer in just going for general strength. Keep the sport specific training for practice.
Have you considered trying this? Obviously it's important to obtain the adolescents legally.