I had the same problem coming out of high school and ended up getting injury more easily because of no “elasticity”. I fixed the problem by having my coach monitor my cleans, snatches, or whatever olympic lift like that… and he would make sure I was bouncy with it on the catch. So when I was cleaning or snatching I was very stiff, I didn’t really absorb the weight I just caught it in an isometric contraction with my legs. So watch this athlete do his cleans or whatever olympic lift, and see if he is too “stiff”. This athlete may be different than me, so it may be something else. Also, jumping on a trampoline helps the feeling of being elastic…the more of an elastic jumper I am on the trampoline I can go much higher than being a “stiff non elastic jumper”. So maybe have this athlete get the feeling of being elastic with that or a pogo stick might work as well. Just some thoughts from personal experience.