These are rapid back-and-forth shuttles with one step in between direction changes. Go two steps to the right, then two to the left.
This really focuses on lateral change of direction, and it's a great way to improve coordination and leg strength/power while building structural integrity in the lower body. Higher reps will scorch your quads and lungs.
Sometimes I think that I've been coaching and training so long that I just take for granted this thing called "experience". As an athlete, I always felt that w? wasted up to an hour of practice doing this thing called a "warm-up".