Ballistic stretching uses the momentum of a moving body or a limb in an attempt to force it beyond its normal range of motion. This is different from dynamic stretching, which involves controlled gradual stretching up to but not beyond the normal range of movement.
An example of ballistic stretching is bouncing up and down repeatedly to touch your toes. This type of stretching is generally not considered useful and can lead to injury as it does not allow your muscles to adjust to, and relax in, the stretched position. Conversely, it may cause them to tighten up by repeatedly activating the stretch reflex. However, if your sporting event requires a ballistic movement, then it may be appropriate and perhaps necessary to conduct ballistic stretching exercises as part of your preparation.