Anti-rotation exercises prevent the spine from rotation or twisting, which is especially important for your lower back.  Whether your athlete is a rotation based athlete or not, core training should include anti-rotation and rotation based exercises. Core muscles are supposed to brace your spine for stability.  The core needs to be trained in multiple ranges of motions and anti-motion.  The thoracic spine (middle of your spine) needs to be trained for mobility as it should allow for up to 70 degrees of rotation or 6 to 9 degrees per segment.

This video gives you several exercises for anti-rotation. These movements are great for youth athletes. At the end of hte video you will be given a great exercise to strength the side body.