Left handed boxers will often fight with right hand, right foot forward. Traditionally, coaches would turn them around to fight orthodox, but southpaw fighters have become more common in recent years. The term actually comes from baseball where pitchers throw from east to west. That is so that when games are played in the afternoon they aren't pitching into the sun. Thus, in the northern hemispere, right-handed pitchers throw with their arm to the north, left handers to the south - hence southpaw.
a left-handed pitcher. The term comes from the common practice of arranging fields so that home plate is west of the pitcher's mound so that the sun won't be in the batters' eyes as it sets, which orients the pitcher so his left arm is on his south side.