Single leg squat to box.
Single leg squat to box is a great start to progressing towards doing a pistol squat. It's also a great exercise for training for any outdoor sport.
Whatever we do, walking, cycling, swimming, running or trail running we don't use both legs together otherwise we'd be hopping like kangaroos. We use our legs separately and when we move we are rarely standing with tow feet planted.
Single leg squats are a great way to generate power one leg at a time, whilst improving balance and stability.