The leg sweeps begin right after the punch at 2:40 in my go-to video of Chen Bing. He sweeps first with the left leg, then with the right, then sets up for another punch at 2:44.
The footwork: He turns the left foot in, turns onto the right and sweeps the left leg around. He’s now facing away, so he’s made a 3/4 turn. He pivots on the left and sweeps the right leg around. That’s another 3/4 turn, for a total 1 and 1/2 turns. He rises on both feet, then sets up for the punch right-left.
After he turns the left foot in, he drops down to a low squat on the right and touches down with both hands while sweeping the extended left leg around (above). He shifts into a left squat, hands still on the ground, while he sweeps the right foot around (below).
Happily, Master Gohring, who by the way is now Grand Master Gohring (8th degree!), is offering us an upright modified version of this move. The footwork is pretty much the same: left-right-left, left-right-left (and then right left for the punch). The sweep is just a swing of the leg.
Between the speed, the deep squats, and the turning, there’s significant potential for knee injury on this move (in my opinion), especially for older students like me. I for one will probably experiment with the sweep shown above, but I doubt I’ll try it at full speed any time soon. I am happy about the modified option!