Knock him on his "bal sege"

Posted by ESC on December 24, 2000

I picked up a "true crime" book at my local library to get myself in the Christmas mood. I came across an interesting phrase:
"When Joe Gere was a small child in Appalachia, his family lifestyle was as Hungarian as if he'd lived in Budapest. In bituminous coal towns like Pursglove, West Virginia (population two hundred), the citizens were classified as 'wops,' 'Johnny Bulls,' 'micks,' 'Polocks' and other racist names. Hungarians were 'hunkies.' Second-generation Americans like little Joey were taught to stand straight when they were called such names, and if the insult was repeated, they were instructed to knock the offender on his 'bal sege,' a family phrase which was pronounced 'ball sheggee' and meant 'left ass.'" From "salt of the Earth: One Family's journey Through the Violent American Landscape" by Jack Olsen (St. Martin's Press, New York, 1996).

My question is: why "left"?