The LOOGY was a phenomenon that exploded in the late 1980's/early 1990's after being an experiment for years before that. The idea was for a team to keep a left-handed reliever as a specialist to get left-handed batters out in the later innings. Tony Fossas was one of the first players that I remember that made a career out of being a left-handed specialist, and of course since he was so successful against lefties and he started around the time that I was just getting into baseball, he was a player that I really liked. It seemed like Boston had a very effective weapon to employ in the later innings.
Fossas was a 31-year-old rookie for the Milwaukee Brewers when he was finally able to crack the Major Leagues for good in 1989. He was signed as a free agent by the Red Sox in 1991 and was immediately inserted into the bullpen as more of an all-purpose reliever. It was not until later that he became a specialist. He was reasonably successful in 1991, going 3-2 with a 3.47 ERA, though he walked nearly as many as he struck out. He did have a rather pronounced platoon split though with right-handers hitting .266/.372/.347 and lefties hitting .190/.277/.298.
It was 1992 that Fossas found his true baseball purpose. That year Boston greatly limited his exposure to right-handed batters, which was good because they hit .345 against him in 67 plate appearances. He walked 11 right-handers and only struck out three. But lefties only hit .214 against him and struck out 16 times, versus just three walks. Fossas was even better against lefties in 1993, but struggled quite a bit against right-handers, which ballooned his ERA to 5.18 on the season as opposed to the 2.43 that he had in 1992.
1994 was Fossas's final season with the Red Sox, and that season was more of the same. He was incredibly effective against left-handers but extremely hittable against right-handers. For his Red Sox career, Fossas went 7-5 with a 3.98 ERA and struck out 118 versus 72 walks in 160.2 innings over 239 games. And therein lies the most interesting aspect of the LOOGY. He pitched against just one batter so many times that he had 80 more games than innings pitched. Fossas went on to pitch another five years for five teams. As a very effective LOOGY, he was always in demand. There have not been many LOOGYs better than Fossas over the years.