On-base plus slugging

On-base plus slugging (OPS) is a sabermetric baseball statistic calculated as the sum of a player's on-base percentage (OBP) and slugging percentage (SLG), designed to represent both the ability to reach base and the ability to hit for power.

Calculation and Formula

The OPS statistic is derived by simply adding two distinct offensive metrics: on-base percentage and slugging percentage.

On-base percentage measures how frequently a batter reaches base per plate appearance. It is calculated using the following formula:
OBP = (Hits + Bases on Balls + Hit by Pitch) / (At Bats + Bases on Balls + Hit by Pitch + Sacrifice Flies)

Slugging percentage represents the total number of bases a player records per at-bat, reflecting their power-hitting capability. It is calculated as:
SLG = Total Bases / At Bats

Therefore, the formula for OPS is:
OPS = OBP + SLG

Because OBP and SLG are expressed as decimals (typically to three decimal places), OPS is also expressed as a decimal. An OPS of .800 or higher in Major League Baseball (MLB) is generally considered excellent, while an OPS above .900 is indicative of an elite hitter.

Significance and Usage

Before the widespread adoption of sabermetrics, batting average was the primary metric used to evaluate a hitter's offensive contribution. However, batting average ignores crucial offensive events such as walks and extra-base hits. OPS was developed to provide a more comprehensive snapshot of a player's overall offensive value by combining the two most critical components of run creation: getting on base and advancing runners via extra-base hits.

Statistical analyses have consistently shown that OPS correlates very strongly with team run production. Because of its simplicity and strong correlation with runs scored, OPS became one of the first advanced statistics to gain mainstream acceptance among baseball fans, media, and front offices. It is frequently used in MVP voting, contract negotiations, and historical player comparisons.

OPS+ (Adjusted OPS)

While raw OPS is a useful metric, it does not account for external factors such as the ballpark in which a player plays or the overall offensive environment of the league in a given year. To address this, statisticians developed OPS+, an adjusted version of the statistic.

OPS+ normalizes a player's OPS relative to the league average and adjusts for park factors. The league average OPS+ is always set to 100. A player with an OPS+ of 150 is considered to have been 50% better than the league average hitter, while an OPS+ of 80 indicates a player who was 20% worse than average. This adjustment allows for more accurate comparisons between players from different eras and those who play in vastly different home stadiums, such as the hitter-friendly Coors Field versus the pitcher-friendly T-Mobile Park.

Historical Context and Records

The conceptual foundation for OPS was laid by early sabermetricians, most notably Bill James, who sought to quantify the true value of offensive events. While James popularized the underlying principles, the specific term "OPS" and its widespread adoption grew throughout the 1980s and 1990s, eventually becoming a staple on baseball cards and broadcast graphics by the early 2000s.

In Major League Baseball history, Babe Ruth holds the highest career OPS at 1.1636, followed closely by Ted Williams (1.1157) and Lou Gehrig (1.0798). Barry Bonds holds the record for the highest single-season OPS, posting a staggering 1.4217 in 2004, a year in which he also set the single-season OBP record (.609). Other notable single-season performances include Babe Ruth's 1.3791 in 1920 and Ted Williams' 1.3791 in 1941.

Criticisms and Limitations

Despite its popularity, OPS is not without its flaws and has faced criticism from modern statisticians. The primary criticism is that OPS weights on-base percentage and slugging percentage equally, simply adding them together. However, linear weights and run expectancy models demonstrate that getting on base is roughly 1.8 times more valuable to run creation than hitting for power. By treating them as equal, OPS slightly overvalues power hitters and undervalues players with high on-base skills but lower slugging.

Furthermore, raw OPS does not account for league context or park effects, which can skew evaluations if not carefully monitored. To resolve these mathematical imperfections, modern analytics have largely transitioned to weighted On-Base Average (wOBA). wOBA assigns specific linear weights to every offensive event (e.g., a walk, a single, a home run) based on their actual run value, providing a more mathematically accurate measure of a player's total offensive contribution. Nevertheless, due to its simplicity and established history, OPS remains one of the most widely recognized and utilized baseball statistics today.