In baseball statistics, slugging percentage (abbreviated SLG) is a popular measure of the power of a hitter. It is calculated as total bases divided by at bats:
where AB is the number of atbats for a given player, and 1B, 2B, 3B, and HR are the number of singles, doubles, triples, and home runs, respectively. Walks are specifically excluded from this calculation.
For example, in 1920, Babe Ruth played his first season for the New York Yankees. In 458 at bats, Ruth had 172 hits, comprising 73 singles, 36 doubles, 9 triples, and 54 home runs, which brings the total base count to 73 + (36 × 2) + (9 × 3) + (54 × 4) = 388. His total number of bases (388) divided by his total atbats (458) is .847, his slugging percentage for the season. The next year he slugged .846, and these records went unbroken until 2001, when Barry Bonds achieved 411 bases in 476 atbats, bringing his slugging percentage to .863, unmatched since.
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Long after it was first invented, slugging percentage gained new significance when baseball analysts realized that it combined with onbase percentage (OBP) to form a very good measure of a player's overall offensive production (in fact, OBP + SLG was originally referred to as "production" by baseball writer and statistician Bill James). A predecessor metric was developed by Branch Rickey in 1954. Rickey, in Life magazine, suggested that combining OBP with what he called "extra base power" (EBP) would give a better indicator of player performance than typical Triple Crown stats. EBP was a predecessor to slugging percentage.^{[1]}
Allen Barra and George Ignatin were early adopters in combining the two modernday statistics, multiplying them together to form what is now known as "SLOB" (Slugging × OnBase).^{[2]} Bill James applied this principle to his runs created formula several years later (and perhaps independently), essentially multiplying SLOB × AtBats to create the formula:
In 1984, Pete Palmer and John Thorn developed perhaps the most widespread means of combining slugging and onbase percentage: OPS. "OPS" simply stands for "onbase plus slugging", and is a simple addition of the two values. Because it is easy to calculate, OPS has been used with increased frequency in recent years as a shorthand form to evaluate contributions as a batter.
The maximum numerically possible slugging percentage is 4.000. Several players (99 as of April 2009) have momentarily obtained this as a career average by homering in their first major league atbat. However, only Kevin Kouzmanoff, then playing for the Cleveland Indians, has hit a grand slam on his first majorleague received pitch, which he did off a Texas Rangers pitcher on September 2, 2006. He thus briefly achieved the best possible career offensive percentage in every category, including some esoteric categories such as "runs per received pitch" (4.000).
Seattle Mariners pitcher Félix Hernández hit a grand slam in his only atbat in 2008. His slugging percentage for the year was 4.000.^{[3]}

