Merrium-Webster gives the following definition of "outlier": a statistical observation that is markedly different in value from the others of the sample. In baseball lingo, an outlier is a season by a player that defies that player's norms by a wide margin. The one that stands out the most in peoples' minds is Brady Anderson and his 50 homer season. But outliers happen often and they have led to a lot of general managers making fools of themselves thinking a player is going to have a season like that again. What follows isn't by any means a comprehensive list of outliers over the years, but just a few that have caught this Fan's imagination.
Darrell Porter (1979 - Royals): Darrell Porter was a number one pick for the Milwaukee Brewers in 1970. He made his major league debut a year later and then played parts of 17 seasons in MLB. He was a very good offensive catcher, prone to passed balls and fair at throwing out runners. He finished his career with a 113 OPS+, so he was above average in every way. But he was never considered an elite catcher. But 1979 was different. In that year, he became one of only a handful of players to walk over 100 times, drive in over 100 runs with 20 homers or less. His walk total was the only year he finished over 100 and with 121 free passes, his year total was 32 walks higher than any other year. He drove in 112 runs or 32 more than his high in any other season. His batting average was 17 points higher than any other year. His OBP was 21 points higher than any other year. He had his best slugging percentage for any of his full seasons that year and he even scored a triple double on extra base hits with 23 doubles, ten triples and 20 homers. Ten triples for a catcher!? It was the only year he scored 100 runs and he even led the league in sacrifice flies. That's an outlier. It makes sense that he became a free agent in 1980 and signed with the Cardinals. They released him five years later.
Darrell Evans (1973 - Braves): Darrell Evans was a good player for a long, long time. But he never had a season like 1973. The year before, he had hit only 19 homers for the Braves and so it was a huge surprise when he hit 41 in 1973. He only hit 25 the year after and only topped 40 again eleven years later for the Tigers. But it wasn't just the homers. His OBP that year was over .400, the only time that happened in his career. His batting average was .281, the only time he ever batted that high (his career average was .246). He posted career highs in slugging, OPS and OPS+. He even had arguably his best year in the field as a third baseman.
Jon Olerud (1993 - Blue Jays): Jon Olerud is one of the most overlooked players ever. He had a sensational career that fell short of Hall of Fame numbers only because he didn't play long enough. He was always one of the best fielding first baseman in baseball and may rank up there in the all time category. He finished with a career slash line of .295/.398/.465. He hit 500 doubles in his career and drove in over 1200. But Olerud had two outliers. In 1993, he was absolutely robbed of the MVP that year. He batted .362 (.284/..297 the year before and the year after). He had career highs in doubles (54), homers (24), RBIs, Runs, OBP, SLG, OPS and OPS+. It was an amazing season and the Fan watched nearly every one of his games that year. His season for the Mets in 1998 was a rare second outlier. Olerud was so good in 1993 that he was walked intentionally 33 times.
Bill Swift (1993 - Giants): Swift is one of this Fan's all time favorite players because he was born in Maine. He was a first round draft pick for the Mariners in 1984 (the second overall pick of that draft). He had some middling seasons for them both starting and in relief. In 1990, the Mariners converted him exclusively to relief and he responded with two excellent seasons. He saved 17 games in 1991 with a 1.99 ERA. He was then part of a six player trade with the Giants and the Giants changed him back into a starter. He did very well in 1992 but didn't have the wins to show for how well he pitched. But in 1993, Swift exploded into a 21 game winner. It was his only season with more than 11 wins. It was his only season with more than 77 strikeouts (he had 157 that year). It was the only season his K/BB ratio was over 2.00 (2.85). It was a remarkable year and he came within a whisker of winning the Cy Young Award that season. He is Exhibit A of Dusty Baker's reputation for burning out pitchers.
Okay. The Fan had a bunch of these in mind at the start of this post, but perhaps working 80 hours a week in the mall during yet another Christmas season has simply turned this man's mind to mush. Add some more in the comments and we'll do some exploring together.