A backwards roll in jujitsu is a fundamental movement used for both defence and mobility. Here’s a description of how to perform a backwards roll:

1. Starting Position: Begin seated on the mat with your knees bent and feet flat on the floor. Your hands can be placed on the mat beside your hips for balance.
2. Tuck Your Chin: To protect your neck, tuck your chin towards your chest. This will prevent your head from hitting the mat as you roll.
3. Initiate the Roll: Start the roll by leaning back, keeping your chin tucked. Use the momentum to lift your hips and bring your knees towards your chest.
4. Roll Over the Shoulder: As you continue to roll backwards, shift your weight slightly to one side so that you roll over your shoulder rather than directly over your head. This helps avoid pressure on your neck and keeps the roll smooth.
5. Complete the Roll: Continue the roll until your feet touch the mat behind you. Ideally, you’ll land in a position where you can continue moving, either by standing up or transitioning into another technique.
6. Control and Balance: As you come out of the roll, use your hands and core to control your balance and prepare for the next move, whether it’s standing up or transitioning to another guard position.

In a jujitsu context, backwards rolls are often used to escape bad positions, regain guard, or set up sweeps and submissions. They are a key part of maintaining fluidity and mobility on the ground.