also baulk, Middle English balke, from Old English balca "ridge, bank," from or influenced by Old Norse balkr "ridge of land," especially between two plowed furrows, both from Proto-Germanic *balkon- (source also of Old Saxon balko, Danish bjelke, Old Frisian balka, Old High German balcho, German Balken "beam, rafter"), from PIE root *bhelg- "beam, plank" (source also of Latin fulcire "to prop up, support," fulcrum "bedpost;" Lithuanian balžiena "cross-bar;" and possibly Greek phalanx "trunk, log, line of battle"). Italian balco "a beam" is from Germanic (see balcony).
In old use especially "an unplowed strip in a field, often along and marking a boundary." The modern senses are figurative, representing the balk as a hindrance or obstruction (see balk (v.)), or else the notion of "a piece missed in plowing" as "a blunder, a failure." Hence, in baseball, "a motion made by the pitcher as if to deliver the ball, but without doing so," attested from 1845, probably from the plowing sense.