When you do whatever you have to do to win, short of cheating, but playing dirty.
This derives from the final fight of "Karate Kid" where the main character's leg is broken and the evil Sensai instructs his student to "Sweep the leg" out from under him to win.
If the pitcher wants to get past a good hitter in baseball and throws a fastball at his face, making him walk, and possibly taking him out for the rest of the game, that is an example of "Sweep-the-leg"
Jess is sleeping. Angus strolls in and engages in the "dick on the leg mack" by sneakily lays his member on her heaving thigh. Jess wakes up and spying such an appetising morsel indulges in an early morningprotein shake.
Typically used in a business environment, it refers to co-workers sucking up to the boss, as in a dog humping his owner's leg. Time spent doing such is known as "OTL time". Basically, another way of saying "kissing ass".
Q:"Where's Jim?" A:"I think he is in the boss's office...probably on the leg".
Q:"Ready to head home?" A:"Naw...I gotta go down to the boss's office and get some OTL time in".
"If you want to get a raise this year, you better get on the leg as reviews are coming up here shortly"
Under the leg, or UTL for short, refers generally to one having a masty under the leg. If you are unaware of the word masty, then fuck off. However, every day tasks are also done under the leg for amusement.
'Aw mate, I just had an under the leg in a primary school'