also: さそく
noun
left foot
Refers specifically to the left foot, as opposed to the leg. In many contexts, 左足 can also imply the left leg, but this sense focuses on the foot.
左足の靴がきつい。
The left shoe is tight.
彼は左足でボールを蹴った。
He kicked the ball with his left foot.
noun
left leg
Refers to the entire left leg, from hip to foot. Often used when the distinction between foot and leg is not important, or when context makes it clear.
左足を骨折した。
I broke my left leg.
左足がしびれている。
My left leg is numb.