Andrew Smith is a 3rd-degree BJJ black belt based out of Richmond, VA (Revolution BJJ). He runs BJJ Path, a video tutorial website.
The Leg Staple or "Knee Drive"
The leg staple guard pass is probably the first guard pass I learned (in judo, no less), and it was definitely the first pass I was comfortable trying on my training partners and in tournaments. The history of this pass goes back at least to the end of the 19th century, and almost certainly back to long before that. In more recent times, it has developed around what your opponent is likely to do as a counter or defense, and it has become a staple of any white belt's BJJ game (if it's not a staple of your game, it really should be). Let's take a look at the essence of this position, along with some tweaks to help execute the technique against a more feisty, technical opponent. Note: this pass is also commonly called the "same-side knee drive pass" as well.
Once the guard has been opened, and you are now in combat base, let's say your left leg is forward. The first thing to do is to look for your partner's right knee to drop down a bit (typically, they are shrimping or "hipping out" to their left when this happens). This concept is the opposite of the knee cut pass, where you'd look for the opposite side knee to drop. As soon as your left knee slides across so that you can pin your partner's thigh with your shin, keeping your foot inside of their thigh, lift your right knee up so that you prop your partner's left leg up, preventing a large portion of their counters to this technique.
Upper Body Control
Once you have your partner's hips under control (when you have created the leg staple along with the shelf with your opposite leg), then next thing to do is to seek out upper body control. Start by hugging your partner's head (here, it's Daniel's right arm that hugs), and use your head to flatten your partner's shoulder out (the less they can turn in toward you, the easier your job is). To finish, step backward so that you are sitting on the floor, leaving only your foot behind. Now just block your partner's hip, then pull your foot free, keeping a tight connection and preventing any guard recovery shenanigans.
Dealing With the Scissor
A very common counter for your partner to use when you've already gotten the first part of the move in place (the leg staple itself) is to slide a shin across your chest or midsection, essentially a "scissor hook." While this can be an excellent guard recovery mechanism, it can also lead you right into the nuts and bolts of this pass. Start by making a big circle with your hand around and then under your partner's foot. Be sure not to simply reach back, as this will allow your shoulders to turn (and your balance to be lost). Once here, you can slide your arm down so that you are controlling your partner's hip, not just their knee or shin. This allows you to pass to either side (either the original method of hugging the head, or a more "double under" guard pass position, where you drive to the opposite side by stacking.
Over/Under Finish Options
Here's another quick look at the 'back door" option to this pass. When you feel like the basic option isn't in the cards (from the over/under stack), turning the corner and going around your partner's guard is the basic gist here. Remember to keep consistent pressure coming forward, driving your shoulder into the back of your partner's thigh, ultimately trying to bring their knee to their nose. Finally, just backstep to alleviate your partner's pressure (and finish the guard pass).
This guard pass has long been a staple in BJJ, and while the knee cut pass has become much more popular, this one can be thought of as a natural compliment, depending on your partner's reaction from the initial guard opening. From there, the two go hand in hand. You will also find this fundamental pass opening up from many other positions like half guard, and it's the essential ingredient in many combat base leglocks. As always, please let me know how this technique works for you!