balk (n.)
also baulk, 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 balziena "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." Modern senses are figurative, representing the balk as a hindrance or obstruction (see balk (v.)). In baseball, "a motion made by the pitcher as if to deliver the ball, but without doing so," first attested 1845 perhaps from the notion of "a piece missed in plowing" as "a blunder, a failure."
balk (v.)
late 14c., "to leave an unplowed ridge when plowing," from balk (n.). Extended meaning "to omit, intentionally neglect" is mid-15c. Most modern senses are figurative, from the notion of a balk in the fields as a hindrance or obstruction: sense of "stop short in one's course" (as a horse confronted with an obstacle) is late 15c.; that of "to refuse" is 1580s. Related: Balked; balking.