The origin of the term southpaw reaches all the way back in time to, well, baseball.
All baseball diamonds are created equal: the pitcher faces west, the batter faces east. This helps the batter survive a careening pitch by keeping the setting sun out of his eyes.
It also means that the pitcher’s left hand will be at his south side, hence the term “southpaw.” The term was coined by Charles Seymour, a Chicago sportswriter.