The B-fly Guard can be a tricky position in No-Gi Grappling because you lack the grips that the kimono gives.
In the video below they demonstrate a half butterfly sweep using a deep underhook.
Once they have the deep underhook they lock their hands with a Gable grip around the far side of the opponent's neck. Utilizing the clinch you can break your opponent's posture and disrupt their base which paves the way for the sweep.
