Southpaw is a boxing term that designates the stance where the boxer has his right hand and right foot forward, leading with right jabs, and following with a left cross right hook. Southpaw is the normal stance for a left-handed boxer. The corresponding designation for a right-handed boxer is orthodox, and is generally a mirror-image of the southpaw stance.
Left-handed boxers are usually taught to fight in a southpaw stance, but right-handed fighters also fight in the southpaw stance. This may give the southpaw fighter a strategic advantage because of the tactical and cognitive difficulties of coping with a fighter who moves in a mirror-reverse of the norm. One reason some left-handed fighters are brought up fighting in the orthodox stance is because of a perception that boxing from an atypical stance (or attempting to learn to do so) would be a disadvantage to the fighter. Another reason some left-handed fighters are brought up fighting in the orthodox stance is due to the (real or perceived) limited number of trainers who specialize in training the southpaw stance.
A skilled right-hander, such as Roy Jones Jr. or Marvin Hagler may switch to the left-handed (southpaw) stance to take advantage of the fact that most fighters lack experience against lefties. In addition, a right-hander in southpaw with a powerful left cross obtains an explosively different combination. The converted southpaw may use a right jab followed by a left cross, with the intention of making the opponent slip to the outside of his left side. Then the converted right-hander can simply turn his body left and face his opponent, placing him in orthodox, and follow up with an unexpected right cross. If the southpaw fighter is right-hand dominant with a strong left cross, this puts the opponent in danger of knockout from each punch in the combination, as jabs with the power hand can stun or knock out (KO) in heavier weight classes.
While rare, the reverse is also true for left-handers; left-hand dominant fighters like Oscar De La Hoya and Miguel Cotto who fight from an orthodox stance give up the so-called "southpaw advantage" strategically, but are gifted with heavier lead hands. Consequently, in MMA if one stands in a southpaw stance (strongside forward), one must train one's cross and left low kick to make it fast, hard and dangerous.
Previous uses of the term southpaw
Though many claim that the term originated due to the orientation of baseball playing fields in order to keep the sun out of the players' eyes and the resulting alignment of a left-handed pitcher's throwing arm, the term had been used decades prior to that to indicate "not-usual".