Front Leg Sweep
See the opportunity. The leg sweep is best done when your opponent has one leg forward and his or her weight partially on it. Don't be fooled by a disguised cat stance, in which one leg is forward but all your opponent's weight is on the back leg--this is a trap designed to lure you closer before delivering a front-leg kick.
Move forward, inside your opponent's reach. You can do this easily by delivering a punch as you move, which forces your opponent to block.
Place your front foot next to and inside your opponent's front foot. Your big toe should be almost touching your opponent's heel. Don't leave too much space between your foot and your opponent's or he or she will see the sweep coming.
Sweep your foot toward your other knee in an arc, contacting your opponent's foot beneath the ankle bone while your foot is still on the floor. Use your foot to lift your opponent's foot from the floor.
Deliver your blow. Your opponent will flail his or her arms to regain balance and keep from falling down, leaving his or her head and torso unprotected.
Back Leg Sweep
Penetrate your opponent's defenses. This is most easily done using a grabbing technique that immobilizes your opponent long enough for you to move forward until your hips are in contact.
Move your forward foot behind your opponent's back foot. This should be your right foot behind your opponent's right foot (or vice versa) so you will be slightly turned away from your opponent, protecting your center. Your heel should be in contact with your opponent's heel.
Adopt a forward stance. Without lifting your foot from the floor, suddenly sweep it back until it is the back foot of a forward stance. Your opponent's leg will be lifted from the floor and he or she will be helpless.
Take your opponent to the floor. Once he or she is off balance, you can let go of your opponent and let him or her drop to the floor. Or you can hang on and lower yourself on top, placing your opponent in an arm bar while you deliver a blow to the head or ribs. You can also choose to perform the sweep so your forward stance is at an angle to your original position, allowing you to turn to the outside and throw your opponent.