This is one of my favorite adductor and hamstring stretches. Dynamic stretching is my favorite way to warm up. You can do it fast, you can incorporate movements you plan to perform, and you can prime your muscles + nervous system for exercise. Dynamic stretching is better than static stretching before exercise or sports, because it helps to preserve muscle force and velocity.
Add this movement in for as little as a minute prior to squatting, sprinting, golfing, or any activity that demands lower body flexibility. Trust me you'll reap the benefits.
1) You're stretching the adductors and hamstrings and calves on the leg that is staying straight
2) You're priming the nervous system with this neurodynamic movement of the posterior chain
3) Staying back on your heel, on the leg that is bending - you're loading and waking up the glutes
4) Pushing your knee outside your foot as you lower into the stretch will promote hip external rotation - a motion that will help your squat depth.