Hold your shape and block. Stay big and on your feet, and get a body or leg in the way as he strikes from close range.
The defender starts tight to the shooter and blocks the shot from close range. Emphasise staying big, on the feet, and committing to the block. Keep it simple until the block is a habit. Rotate the roles.
Fork it into your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block.