Since 1900, 819 men have played in enough major league games to accumulate at least 5,000 plate appearances. These 819 players, obviously none of whom are pitchers, all had legitimate major league careers managing to stick around on a major league roster for at least eight years as a full time player, or at least 10-12 years as a part time player. These players include some who were great hitters, such as Babe Ruth, Ted Williams, Lou Gehrig, some who were great all around players such as Willie Mays or Honus Wagner and some who managed to have a long major league career primarily due to their defensive ability. Players of this type include Mark Belanger, Nefi Perez and Sandy Alomar.
Of these 819 players, 14% threw, or throws, left-handed. This number may be slightly higher than most estimates of the proportion of various populations that are left-handed, but it is not dramatically different. Left-handed throwers are not, however, spread evenly over this group of players. Obviously, they are concentrated almost entirely at a few positions, designated hitter, first base and the outfield. More strikingly, the left-handed throwers in this group are, collectively, much better hitters. The median OPS+ for the 819 players is 109. This makes sense as players who play for long enough to come to the plate can be expected, as a group, to be better than average hitters. However, among left-handed throwers, the median OPS+ is 119. The median hitter among left-handed throwers for this group is Mark Grace, who was a very good hitter for many years. For right handed throwers, the median is 108 held by nineteen hitters including Rico Petrocelli, Ralph Garr and Jose Vidro. This is a good group of players, but as hitters, clearly several cuts below Mark Grace.
These 819 players can be divided into four groups based on their offensive production. The first, which includes players with a career OPS+ of 120 or better; the second had OPS+ of 101-120; the third had an OPS+ of 81-100, and the fourth all had OPS+ of less than 80. Broadly speaking these categories consist of excellent hitters, average to above average hitters, weaker hitters and poor hitters. Not surprisingly, the relationship between higher OPS+ and likelihood of being in one of the better offensive groups is direct. 23% of the top hitters threw left-handed, but the proportion fell to 16% with the average to above average hitters, and six percent for the below average hitters. In the worst hitting group only one out of 50 players threw left-handed. That player was Omar Moreno who had an OPS+ of 79 and was, for much of his career viewed as a better offensive player than he was because he stole a lot of bases and hit for a decent batting average.
If different measures of offensive ability are used, or if the players are broken down into different groups, the basic finding remains the same. Players who throw with their left-hand who want to have legitimate big league careers must either pitch or hit, but right-handed throwers have a third option, they can succeed in the big leagues with their gloves. While defense is valued in left-handed throwers, it is almost never enough to facilitate a long big league career.
This is not exactly an earth shattering observation as anybody who pays attention to big league baseball probably could have figured this out just by looking at most major league rosters either now or at any time in the last century or so. Nonetheless, the data is startling as only 14 left-handed throwing players have had lasting big league careers, other than as pitchers, while being below average hitters.
The finding suggests that left-handed and right-handed throwers are, to some extent, playing different games at the big league level, and therefore has implications for player development starting at a very young age. One of the first baseball skills that young children master is fielding. This may be because it is easier than hitting or more likely because it is easier for coaches and parents to practice and teach. Nonetheless, among seven or eight year olds, the better players first begin to stand out because they are good at fielding ground balls. The hitting generally comes a little later, so within a few years the fielders who can hit begin to stand out from those who cannot. However, there are still plenty of ways a good fielder can contribute to a team and be valuable as (s)he gets older. For left-handed throwers, these options disappear usually by high school when traditional views about what position lefties can play become more powerful.
Thus, a good fielding right-handed thrower can succeed in high school and even beyond as a relatively weak hitter, but a left-handed thrower cannot. The finding from the Major League data is applicable, although probably to a lesser degree beginning at the high school level, and certainly by college. Left-handed throwers are better off focusing on pitching and hitting from a young age because this is how they will work their way into lineups and rosters. The ability to field is valuable even for a lefty, but the reality is that almost no left-handed thrower has built a major league career based largely on great defense.