Balance is defined as keeping someone’s center of mass within their base of support. When the center of mass moves outside the base of support they become unbalanced.
Everyone has 3 muscle strategies to become balanced again: ankles, hip, stepping (reaching).
All sweeps involve the attacker unbalancing an opponent so they can be tipped over and gaining the positional advantage. Judo does a better job than Jiu Jitsu of teaching Kuzushi, the art of unbalancing.
YOU MUST UNBALANCE prior to sweeping. If you feel you are muscling a sweep then the opponent was not sufficiently unbalanced.
While this principle works for all sweeps, the X-Guard is probably the easiest position to understand unbalancing for Jiu Jitsu. Here my instructor Gustavo Gasperin, @mmaleech, has control of both of my legs / base of support. Prior to initiating a sweep he must disrupt my base first. While being unbalanced there are 3 directions to sweep depending on my response.
When you learn how to unbalance your opponent your sweeps will be effortless.
Dr. Mike Piekarski, DPT
BJJ Brown Belt
Former MMA Fighter