This is another way to look at flexibility. You can look at flexibility as the range of motion around a joint that you can control - certainly valid. You can also look at it as the correct amount of motion through the required range of motion, at the correct in the correct plane at the correct time – also valid. But a simpler way might be to use the paradigm of shapes inspired by Eyal Lederman in his book Therapeutic Stretching. What shapes do you have to make in your sport and what shapes can you make. The task is to reconcile any difference between those two. This is a simple concept but very effective in application that is easy to see, to explain and to train. Best of all the athletes get it immediately.