This is a safety bar squat variation named for its creator, Fred Hatfield, that allows the lifter to provide support and assistance with the arms.
Perform a safety bar squat while holding another barbell in a rack or the rack itself at around stomach level. Use the arms to provide needed assistance in stabilizing and/or recovering from the bottom.
The Hatfield squat gives athletes the ability to continue squatting during periods of injury or limitations that prevent them from squatting normally by allowing self-assistance to help through painful or restricted segments, or simply as a temporary psychological bolster.
It can also be used to load the eccentric motion heavier than would be possible in a normal and without partner assistance. By assisting the concentric motion with the arms, the weight can be increased somewhat to overload the descent.
These can be programmed as you would any other primary squat variation—they will typically only be used as a temporary substitute for back and front squats as needed. Because this will usually be during periods of injury, select weight by feel rather than trying to predict percentages.