Plate Knee Tucks
This is another great exercise to do with limited equipment or with beginner athletes. As a variation of mountain climbers, it would work great for wrestlers, gymnasts and swimmers/divers.
Start with both feet on a plate. Make sure you are on a surface where the plate can slide fairly easily. Keeping all your body weight on your hands and shoulders, tuck your knees to your chest by crunching your abdominal muscles and sliding the plate across the floor. Push your legs back out to the starting position and repeat for reps.