The Double Under Guard Pass
The double under guard pass is a staple of any jiu jitsu practitioner's arsenal. It is a truly fundamental method of getting around the legs, and it's a technique you'll see all the way from white through black belt. While the gist of the technique can be grasped by the novice, there are ample details to keep any advanced jiu jitsu person interested in learning details for years to come. Here are some basic methods of getting under and around the legs, and two different outcomes.
The easiest way to enter into the double unders pass is by first opening the closed guard. Once the guard is open, you will typically enter into a combat base position, from which you can easily enter into any of the four basic ways to pass the guard. Start by diving both arms underneath your partner's hips, particularly if they have raised their legs off the ground in order to play open guard of some kind. Lead with your elbows, not with your hands, and be sure to dive both arms under at the same time, lest you get caught in a triangle choke. Be sure to clasp your hands together, preferably at the wrists. Use the combat base knee that's up to prop your partner's hips off the ground, and grab their lapel with that same arm. Next, apply pressure forward, ensuring that your partner's knee is nearly touching their nose (or, failing a more limber partner, as close as their flexibility will allow). Finally, press your chest forward to clear their legs off to the side. Don't turn away as you're doing this last part!
One ultra-important detail whenever you do a double under pass, is that your arms will always work together as "a team." Never enter with one arm at a time (unless you just enjoy being triangle choked, or are really working on your triangle defenses). Next, when you get your hands (or wrists) clasped together, be sure their legs are all the way up on your shoulders: you really don't want to fight the strength of someone's legs with your arms, but instead with your entire torso. Be sure that, when you elevate their hips, you're able to keep them off the ground by inserting your lead knee under their hips, keeping their hips off the ground. One way to make sure the "knee in the nose" effect works well is to drive forward by getting off of your knees, using a "kickstand" to drive your weight forward. Once you turn the corner and pass the guard, be sure to stabilize your position (side control) before moving on to the finishing submission.
Taking the Back
Another potential outcome from an attempted double under guard pass is taking the back. As you stack your partner by driving their knee to their nose, often times (especially in no-gi), they'll elect to turtle, attempting to escape back to guard, or just to prevent the guard pass. As your partner begins to turn, it's important that you connect your chest to their back, staying heavy here and offering them no space at all. Stay connected as they finish turtling, setting up an easy back take. You can either step over to finish taking the back, or you can pull them into your lap, depending on your partner's reaction and your relative experience level.
Which outcome do you prefer from double under passing?
A word of caution: whenever practicing the double under pass, often also called the "stack pass", be sure your partner's flexibility requirements are not exceeded! In other words, don't hurt your training partner while practicing this technique. We usually only get one neck in life, so we have to help one another protect these things. As always, be sure to let me know if these techniques work well for you!