Old English sceanca "leg, shank, shinbone," specifically, the part of the leg from the knee to the ankle, from Proto-Germanic *skunkia- (source also of Middle Low German schenke, German schenkel "shank, leg"), perhaps literally "that which bends," from PIE root *skeng- "crooked" (source also of Old Norse skakkr "wry, distorted," Greek skazein "to limp"). Shank's mare "one's own legs as a means of transportation" is attested from 1774 (shanks-naig).
1927, in golf, "to strike (the ball) with the heel of the club," from shank (n.). Related: Shanked; shanking. Earlier as "to take to one's legs" (1774, Scottish); "to send off without ceremony" (1816).