Tractor Dragging refers to grabbing someone with your hands and then using your legs to pull them in some manner. Normally the person is pulled either into your center or parallel to your chest wall, but any movement where you grab someone and use your legs to move them might be considered tractor dragging. Here are a couple of ways you might see this done.
Reach forward and use both hands to grab the opponent’s jacket, shirt, or shoulders. Move the back leg until you are at 90° to the person and then, while holding firmly onto them, settle down and back into a strong Kiba Dachi. Depending on the relative positions of you and the other person, this may have the effect of pulling the person over your front leg, causing their calf or shin to be destabilized, or pulling their torso forward of their hips. Usually these conditions will cause the opponent to fall.
Another way you might envision a tractor drag is to establish a Hidari Sochin Dachi facing your opponent at angle 1. Grab the opponent somewhere in the upper torso and then pull your arms directly forward and into your center. Now rotate your torso so you pass through a temporary Kiba Dachi facing angle 7. Continue rotating until you have established a Sochin Dachi facing angle 4. Release your grip as the other person falls.
A final example might be to establish the same Hidari Sochin Dachi and to grab the person in the same manner. Now shift your weight backward to establish a moderate Kokutsu Dachi as you pull the person to your right and then release them as the fall toward angle 6.
All of these methods have a substantial risk of collision with a moving and perhaps aggressive person. As a result we do not consider this movement to be a particularly effective strategy. However, you may find times when using your legs and a sequence of effective stances can pull an opponent down. But you need to remain vigilant against the possibility that they will collide with you in unexpected ways.
The benefit of these movements, when used in this manner, is that they can be done quickly and, when done with sufficient speed and stance integrity, can be very effective. The down side is that these actions are physically demanding on the legs, require precision of movement, will not work well if the other person braces themselves in some manner, and often have associated risks of both collision and the opponent grabbing you as they pass by and begin to fall.
These methods are not always used for Nage. They may also be used simply to alter the structural alignment of another person so that you can then employ further manipulations. In these situations the movements are seldom thought of as tractor dragging because they are much more subtle and utilize smaller movements. But the movements are generally the same and you should recognize them as miniature tractor dragging sequences. In Tensoku Ryu you will find this context for tractor dragging used quite frequently.