Only about 10 percent of the world's population is left-hand dominant. Among professional baseball players, that number skyrockets to about 25 percent, according to the Japan Times. The reason for this disparity can be found in a number of factors, including geometry, physics and architecture. These seemingly minor differences can yield significant advantages over the long run for left-handers, also called "southpaws" in baseball.
Most pitchers are right-handed, as are most batters. When a baseball is thrown from a right-handed pitcher to a right-handed batter, the batter has to look over his shoulder at a ball coming straight at him. This minimizes a batter's depth perception and makes it tougher to assess the speed of the ball when he bats. A left-handed batter, on the other hand, watches the ball leave the right-handed pitcher's hand from a slightly different angle than a right-handed batter, giving him a better side view and, consequently, a better chance to evaluate the speed of the pitch. This slight advantage increases the left-handed batter's ability to follow the pitch and time his hit and will improve his batting average over time.
When a baseball player swings his bat, the momentum of his follow-through turns his torso and sends his momentum away from home plate. A right-handed batter's momentum is directed down the third base line. The problem with this is that, if the batter connects with the ball and has to run to first base, he has to stop his momentum and propel himself in the opposite direction. A left-handed batter, on the other hand, has his momentum swung down the first base line--the direction he needs to run. He can let this momentum carry him in the direction he needs to run. On top of that, a left-handed batter also stands on the right side of home plate--roughly 1.5 meters closer to first base than a right-handed batter stands. This cuts down their travel time to first base by about 1/6 of a second, according to the Japan Times Online.
Park Design Bias
In many ballparks, the right field wall is shorter than the center- and left-field walls. This makes it easier for right-handed batters to pop their ball over the fence for a home run because that is the more difficult side of the park for right-handers to hit toward. However, right-field is where many left-handers tend to pull their hits, and it's the direction that enables them to generate the most power through their swing. As a result, short right-field walls--which are common in many professional ball parks--give a distinct hitting advantage to left-handed batters, particularly sluggers who frequently swing for the fences.