Four Corners is a BJJ solo drill where the practitioner starts in a crab walk position (belly up. feet both firmly on the ground shoulder width apart, and hands flat on the ground shoulder width apart, slightly behind), and transitions into a bear crawl position (belly down, hands on the ground shoulder width apart, feet on the ground behind you, on all fours) by switching to opposite points of contact briefly while the transition occurs (right foot, left hand or left foot, right hand).
This movement should be done fluidly and smoothly, and the directions and tempo can and should be varied throughout the drill. I tend to do this drill at home on the living room floor while watching tv. I don’t set a timer or set reps, and just focus on being able to complete revolutions, direction switches, pauses, and static holds in various stages as smoothly as I possibly can.
Four Corners is easy to practice on most flooring (no need for mats), or on grass or beach sand without getting rugburns or injuring yourself or getting your clothes dirty.
Four Corners helps develop movement patterns relevant to doing sit-outs, duck unders, back takes, knee strikes, and turtling to defend against your guard getting passed.
Adding a few steps of bear crawls or crab walks to the drill can also add some fun and variety to the drill. Be sure to take steps forwards, backwards, to each side, and diagonally.
Props can also be introduced to this drill. Adding yoga blocks, stairs, chairs, or any sturdy device to elevate one or more limbs introduces another fun challenge and more variety to the drill.
https://www.youtube.com/watch?v=jBm4X68c2JQ