Injury Dynamics is a fighting style taught by Chris Ranck-Buhr in San Diego. This shows an example of a coordination set, which is nothing more than a planned series of strikes/injuries. The "reaction partner" mimics the spinal reflexes caused by each strike. These reflexes can't be controlled. They are akin to a person touching a hot stove and retracting their hand. We do it without thinking or the ability to stop it.
The freestyle practice allows you to use whatever strikes you like depending on the targets available to you. Each person takes two turns taking the other to non-functional and then the other person takes their turn--usually starting from the ground.
In these examples, we are moving somewhat faster than normal. Basically you can go as fast as your partner can react as long as you maintain your targeting and balance. When learning we move much slower--almost in slow motion--to imprint hitting the right target each time and every time.
If you find yourself on the West Coast, visit Injury Dynamics--it will change your outlook on fighting no matter what style you hail from.