Under the leg is exactly the same as Under the arm except using a different limb. You can throw a ball under either leg from either hand, so there are four possible ways of performing the trick.
Throwing under the same leg
By throwing under the same leg I mean throwing under the leg that is on the same side as the hand with the ball. The left hand throws under the left leg & the right hand throws under the right leg.
Take one ball & practise throwing it under the leg on the same side as you are throwing from. Try not to bend down while you throw under your leg, stand up straight, lift your leg up as far as you can & extend your normal scooping action under your leg.
Aim your throw to rise up through the centre & peak on the opposite side, throw the ball a little higher to allow yourself a bit more time to get your hand out from under your leg & to put your foot back on the floor. An under the leg throw should be exactly the same as a normal Cascade throw in that it goes underneath the ball before it & is caught with the opposite hand, except that it also passes under your leg.
When you can do it with one ball pick up the other two & fit it into the Cascade. Remember to not bend down for the throw, bring your leg up into the pattern & scoop your arms lower.
You can do one throw at a time, then the same ball every time. When doing every right & every left it is easier to hold your leg off the ground rather than continuously lifting it up & down. Making every throw under the leg is also possible & very energetic. & looks quite daft too. You'll need to throw much higher than usual, look straight up to watch the balls as they peak. It may help to skip from foot to foot bouncing on your toes too.
Throwing under the opposite leg
Exactly the same as before but this time the right hand throws under the left leg & the left hand throws under the right leg.
You can raise your leg with your knee bent or kick across your body with the leg straight for this one, high kicks like the Tiller girls ("Who?" I hear you cry) look very good. You will need to turn your hips towards the throwing arm but keep your head & upper body facing forward. Lift your leg as high as possible & scoop your hands down low for each throw just like before.
When throwing every ball under the opposite leg make sure one leg is out of the way before you move the next one or you will end up bashing your kneecaps. The key is consistent & controlled high throws.
Try mixing opposite & same leg throws in different combinations with a few Under the leg catches for good measure.