We are always telling student in the gym during a squat to send their hips back. It’s one of the main sticking point in being able to do a squat well. This is even more necessary when doing an overhead squat. Placing the weight overhead increases the torque on your hips. To help distribute this weight, the plane of the bar should bisect the body, half your weight should be in front of it and half behind it. The only way for this to happen is to make sure that you send your hip BACK! This will cause you to use all the right muscle, drive your weight through your heels, and get your weight evenly distributed underneath the bar.
In these photos, I’m using my self as an example and below, you can see on the left what happens when you do NOT push your hips back. Your weight ends up on the insides of the balls of your feet, your quads are taking the brunt of the force, and your knees are not over your toes. Most of your weight is in front of the bar. This is a hard position to be in!
The photo on the right is much closer, but not perfect, to a proper overhead squat. The knees and hips are back and the shoulders are much more open. The bar dissects the body weight in half and is a much more stable position. Doing the lift in the most efficient way possible will allow you to lift more!