In the game of cricket, backward square leg is a fielding position that is located between square leg and fine leg on the on side. Unlike most fielding positions in cricket, backward square leg is by definition in the deep, ie, close to the boundary. As such, the only variation is short backward square leg which is located approximately halfway between the boundary and the batter, or even closer. If the fielder is close enough to be regarded as silly, the position would be referred to as silly leg, which is an umbrella term to describe any very-close-in fielding position in the arc from mid-wicket to backward square leg.
Backward square leg is typically a defensive position that is required to stop deflections off the pad or bat, as well as the hook, pull, and sweep. It requires a strong throwing arm as many balls will be fielded close to the boundary, and for this reason is often filled by a fast bowler.