With this move, the practitioner lowers his body, pins around rapidly on the pivot leg, and using his other leg, sweeps out the legs from under his opponent. Many similar moves can be found in Chinese martial arts and the move appears to have come from Kung Fu.
Abridged move description/video courtesy of Suka Pass.
True to the description, the move can be found in many styles of Kung Fu under various names such as "the iron broomstick" or "the tiger's tail". It is also commonly found in Southeast Asian styles such as Silat.
While far from being a commonly used fighting technique, there is a surprising amount of footage of it being used successfully in full contact competition and the streets™.
Foot sweeps and leg sweeps in general work by catch your opponent shifting their balance from one leg to the other and pulling the rug from under them. It's a move that requires good timing and prediction which can't be brute forced unless there's a large size or strength disparity. In grappling arts (and striking arts that allow the clinch), the timing requirement can be eased somewhat as you can push and pull your opponent to get them to step in semi-predictable ways. To pull off the Crawl Cyclone where you have no hands on the opponent, there are 2 methods that can be used to set it up.
#1 - Getting your opponent to take a step
Fighters will often retreat linearly by rapidly backstepping away from the opponent. This happens particularly often in MMA for a medley of reasons that I won't go into here. A fighter going backwards naturally has to shift their weight backwards when taking a step back, which leaves them vulnerable to getting swept by the Crawl Cyclone if hit during this moment.
One example was used in the match between former BW UFC champion Cody Garbrandt and Raphael Assunção.
Garbrandt first uses a wrestling duckwalk to fake as if he's going to shoot a takedown. Assunção responds to the feint by moving backwards out of range of the expected shot. Garbrandt changes levels again as if he's going to shoot, but instead tries to sweep Assunção off his feet. His timing is a little off however as Assunção had managed to set his weight down, so it ends up being a hard leg kick instead of a sweep.
Here's another example from pseudo kickboxing organization Karate Combat.
Cera lunges forward as if he was going to blitz with punches. Ex-UFC veteran James Vick retreats out of the way of the expected blitz. Cera instead drops down and sweeps Vick off his feet.
It can also be executed when your opponent is coming forwards by timing when your opponent is about to plant their foot and sweeping them before they set their weight down. When strikes are on the table though, this is riskier as you run the risk of being over.
#2 - Kicking an opponent on one leg
Any time someone is on one leg, they are off-balancing themselves to some degree. A Crawl Cyclone can be used to great effect to take them the rest of the way down.
A common instance is when a person is throwing a standing kick as they have one leg planted by definition. In the first clip, the Crawl Cyclone is used in a Shooto MMA match. The victim is caught on one leg while throwing a leg kick and is toppled over. In the second clip, Chris Clements catches then-prospect (present day former UFC WW title challenger) Stephen "Wonderboy" Thompson with the Crawl Cyclone while Wonderboy is attempting a hook kick. This is especially effective on Wonderboy as he uses a more bladed side-on stance that leaves him more vulnerable to being swept in that horizontal plane.
Another instance is when a person is checking a kick. Checking is done by raising their shin into the path of a kick so that the kicker hits bone rather than softer muscle (and possibly hurting their leg in the process).
In this clip, Ferguson changes levels, potentially faking a takedown, and instead goes for a Crawl Cyclone. Gaethje lifts his leg to check, but the kick lands low on his ankle rather than his shin, sending him toppling to his hands and knees.
Disadvantages
