Artemis BJJ (MYGYM Bristol), Can Sönmez, Bristol, UK - 15/06/2016
Marcelo Garcia has written that when passing butterfly guard, it's important to keep in mind that "unlike the closed guard or half guard, in the butterfly guard, your opponent is not trying to hold you in place." In my opinion, the ensuing dynamism and movement makes butterfly guard a more advanced position, which requires greater sensitivity and timing than closed or half guard.
So, I stuck with the most basic technique in butterfly, which is the classic butterfly sweep. There are numerous grips to try, but for me there are three main ones: collar and sleeve, deep underhook and the shoulder clamp. Having the collar opens up chokes, as well as providing excellent control to switch into other attacks and sweeps. The shoulder clamp gives you the option of sweeping in either direction (either away from underhook side, or if you can get your arm by their head, leveraging up with your elbow under their head to go towards the underhook), as well as things like pressing armbars and omoplatas.
However, the deep underhook is the way I first learned and I think the easiest one to teach. Saulo calls this the 'competition' grip, I guess because it must have been something he noticed appearing more in competition (as opposed to the collar grip, which he dubs 'classic': interestingly, his personal preference is grabbing the front of the belt, not something I've ever had much success with). You reach under their armpit as far as you can, getting your shoulder in if possible. Secure that arm around their back, or you can grab the belt.
With the legs, it tends to be slightly more straightforward. Either you're going to have both feet hooked under their thighs, with your knees flared out wide, or you'll have one hook in, the other knee on the ground: I'd recommend the latter. That angle helps with the sweep, I find, as well as making it harder for them to drive your back to the mat. In both leg configurations, you want to have your forehead driving into their chest. If they can get their head under yours, that's problematic, because then they can drive you flat on your back and start their pass.
Butterfly also links back to sitting guard, of which butterfly is effectively a short range version. That's because in both, you can put an arm behind you for base and mobility. It makes it harder for them to collapse you to your back, while also enabling you to keep angling off. That sets you up for attacks (especially the butterfly sweep, along with various fun from the underhook, like pressing armbars, back takes etc). Armdrags are another big area for butterfly, though that's a topic for another day.
Whatever grip, the basic mechanics of the sweep are broadly similar. You need to have some kind of control over their arm on the side you want to sweep, otherwise they will be able to post. Grab the sleeve or the wrist, possibly the elbow if you can sufficiently control their lower arm too. Lean back very slightly to get their weight towards you, then drop to your shoulder on the sleeve grabbing arm, lifting as you drop. Switch your legs, bringing one under the other in order to establish scarf hold, heavy on your cross face. If you've lifted them up but they aren't going over, try hopping towards your lifting leg with your other leg. That should eventually provide the leverage to knock them to the mat.
Teaching Notes: On the shoulder clamp, I didn't feel we really got into the importance of sitting up, so I'll focus more on that next time. It is perhaps a bit too complex to squeeze into an hour together with other butterfly grips: possibly something to show in isolation, though I do often teach multiple techniques in the women's class. On pushing the head down, it's important to get the elbow right by the back of the head, as well as keeping your arms in tight. If that starts loosening, they have too much room to move and may be able to pull their head and/or arm free. Gable grip makes it much easier to sweep too: Kirsty was naturally moving into the forearm clasp, which is good for maintaining the grip, but sweeping is tough from there.