Marcelo reiterates the legalities behind entangling an opponent's leg for IBJJF competition: You may 'reap' across an opponent's hip with your foot from the outside as long as you are not controlling their corresponding foot and/or lower-leg by encircling it with your arms in the same manner as an Ankle-Lock. Also, you cannot reap the leg if your opponent is bearing weight onto said foot while their hips are elevated off of the mat, e.g. in a kneeling or standing position. Performing a Scoop-Grip onto their leg while reaping is allowed, i.e. under-hooking the lower leg; this helps facilitate a non-weightbearing posture, therefore mitigating potential injury from an incorrect escape attempt. Lastly, a good Z-Guard often requires that your legs are sufficiently long enough to cross your ankles while framing with your shin.