In baseball, a left-handed specialist (also called, somewhat derisively, a LOOGY or Lefty One Out Guy) is a left-handed relief pitcher who specializes in getting left-handed batters out. These pitchers will commonly only pitch to a very small number of batters in each outing (often just one), and rarely to right-handed batters. Most Major League Baseball teams have a couple of left-handed pitchers in their bullpens, one of whom is probably a left-handed specialist.

The effectiveness of left-handed specialists against left-handed batters is the result of a number of fairly well-defined factors. Since most pitchers are right-handed, left-handed batters naturally have fewer at-bats against, and therefore less experience with, left-handed pitchers. The pitch trajectory from a left-handed pitcher is also reversed and their pitches therefore tend to have a more sweeping effect across the plate, which is harder to hit than the traditional outside-in trajectory from right-handed pitchers. This inexperience and seeming difference in pitch trajectory poses a large problem for many left-handed hitters.

While there are right-handed specialists, the practice is uncommon for a number of reasons. Although their pitches have the same "sweeping" effect against right-handed batters as pitches from lefties have against left-handed batters, since the average batter will face a right-handed pitcher in 70-80% of their at-bats there is more opportunity for right-handed batters to adjust to right-handed pitching than the converse. Also, given this natural inexperience, many left-handed pitchers have altered their pitching delivery to accentuate the "sweeping" nature of their pitches against lefties. While this potential exploitation exists for right-handed pitchers as well, given right-handed batters' ample experience with right-handed pitching, it is usually of relatively little gain.

Because left-handed specialists face few batters, they accumulate a relatively small number of innings pitched during the course of a season. An effective left-handed specialist may consequently enjoy a long career because his pitching arm has suffered less stress than that of other pitchers. The pitcher Jesse Orosco, for example, increasingly became a left-handed specialist late in his career and he pitched in Major League Baseball for 25 seasons, retiring when he was 46 years old.

Noteworthy Major League Baseball left-handed specialists include:

• Alan Embree
• Graeme Lloyd
• Jesse Orosco
• Dan Plesac
• Ricardo Rincon
• Scott Sauerbeck