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 wristlock is one of those submissions that seems to fall through the cracks. You can blame aikido if you'd like (and Steven Seagal movies) for presenting relatively unrealistic scenarios, causing a lot of Brazilian Jiu Jitsu practitioners to conclude that wristlocks must be a low percentage move. The reality is that they're an integral part of a complete BJJ practioner's arsenal of attacks, and understanding that most tournaments allow wristlocks for all adult competitors is really important. It's also great to know what not to do with your hands, so this lesson will take you to a solid understanding of the compression wrist lock, one of the most common types of joint attacks you're likely to encounter across all martial arts.
Closed Guard Entry
Start with your opponent in your closed guard. This is, by far, the lowest risk option you have available, and therefore a fantastic attack to begin working with so that you can better understand the nature of the wristlock as a submission. After all, if you screw everything up, you've still got closed guard (unless you really, really screw up). Assuming your partner has both hands on your midsection (and this is extremely likely, given proper posture in the closed guard), reach up with your right hand and find your partner's funny bone, right behind their elbow, but shy of their triceps. Use your middle and index finger ("Spider-man grips") to start opening your partner's elbow, and then reach up with your left hand right on top of your right hand, reinforcing the grip. Pinch your elbows together to facilitate the trap, and then pull inward as you sit up outwards, crunching your ribs toward your partner's elbow. The general concept here is to bring your partner's knuckles to their forearm. It's worth noting that the wrist takes a great deal less pressure to break than the elbow or shoulder, so be careful!
An alternate way to get the initial bend in the wrist is to reach across with your left hand, cupping the top of the wrist, and adding a fulcrum of sorts to the mix. This will facilitate bending their wrist, but you've got to be careful here as the person may pull their elbow away, given the opportunity and the likely red flags that are going off for them. However, this initial bend trick can be extremely helpful with getting the wristlock initially, and, ultimately, getting good at it over time.
From the Feet
Similarly, you can hit the wristlock right from the standing position. This can be an extremely fast match-ending technique (think: Jacare circa 2003), but it can also cause your partner to sit down, possibly avoiding the submission in doing so (but also possibly not avoiding it at all). You can start with the wrist bend grip if you'd like, or you can go straight into the submission forthwith, especially if your partner already has a slight bend in their wrist. Be extremely careful with this technique in class, as your partner might not understand that there is a very credible submission threat from the feet.
From the Open Guard
Another extremely high percentage attack (for me, anyway) is the wristlock off of a guard pass attempt. As your partner begins to move up your body, ultimately trying to get up to your head or collar for final control, you can utilize the reach to set up a sneaky, nasty wristlock. This is very similar to the attack from standing in the sense that people don't often expect the wristlock, often anticipating guard pass prevention techniques. However, it's worth noting that this attack works extremely well in conjunction with basic guard maintenance.
It's worth repeating that the wrist is an extremely fragile joint. Caution is necessary at all levels and under all circumstances (except self defense), so please think of your partner's safety even more than usual when performing this submission series. The benefit, however, is that you will have an extremely sneaky piece added in to your game once you figure out how to integrate the wrist lock properly. As always, I'd love to hear from you, so let me know if these techniques are working well for you!