Introduction to Advanced Baseball Analytics: OPS+

Mandatory Credit: Vincent Carchietta-USA TODAY Sports

Note: All statistics cited in this article are current up to the June 6, 2022 games

Advances in statistical analysis have transformed the game of baseball in recent years, affecting everything from free agent contracts to defensive alignments. This revolution has been fueled by a dizzying array of numerical tools that typically share a common goal of removing random chance from more traditional measures of success or failure.

For much of the 20thth For the 19th century, so-called “counting statistics” like RBIs and pitcher wins drove baseball’s numerical discourse. However, in the second half of the 20th century, and particularly into the new millennium, keen observers of the game began to see the flaw in this approach: counting statistics can easily be skewed by luck or other circumstances beyond a player’s direct control. For example, RBI totals can be increased simply by hitting in a strong lineup or hitting with many runners on base. A seemingly more objective way of assessing a batter’s ability is On-Base Plus Slugging (OPS), which has the benefit of being a rate statistic that adds up On-Base percentage and Slugging percentage, to get a combined measure of how often a batter hits base and hits for power.

However, OPS also has its weaknesses. For example, as any Mets fan knows, Citi Field has typically favored pitchers since it opened, but OPS alone doesn’t account for baseball stadiums. Additionally, offense so far in baseball’s 2022 season has been in a significant decline, but again, a batsman’s OPS doesn’t reflect that trend. However, there is one increasingly cited and simple statistic that accounts for ballpark factors and league-wide offenses: OPS+, which should be one of the first tools any baseball fan uses when evaluating an individual hitter’s performance.

Let’s take a quick look at how OPS+ is calculated and what it means.

According to that MLB Glossary, “OPS+ takes a player’s on-base plus slugging percentage and normalizes the number across the league. It takes into account external factors such as stadiums. It then adjusts so that a score of 100 is the league average and 150 is 50 percent better than the league average.” For example, in 2021 the league’s OPS average was 0.728. So if we ignore baseball effects for a moment, a player with an OPS of .728 would have an OPS+ of 100 or league average, and a hitter with an OPS of over .728 would also have an OPS+ of over 100.

To account for ball parks in OPS+, an index called Park Factor is used. The park factor is also scaled to 100, with higher numbers indicating a stadium is more offensive and lower values ​​meaning it favors pitchers. During the 2021 season, Citi Field’s park factor was 98. Therefore, since they play half their games in a pitcher-friendly park, Mets hitters would have a higher OPS+ than a player on a team like the Red Sox, whose home field, Fenway Park, had a 105 park factor in 2021, third best on offense.

In fact, during the 2021 season, both New Yorks Peter Alonso and Bostons Xander Bogaerts had an OPS of 0.863. However, Alonso’s OPS+ was 133 while Bogaert’s was just 127.

Statistically, Citi prefers field pitchers, making OPS+ an important tool for making Mets hitters their due.

If we turn our attention to the current 2022 season, the Mets have gotten a lot of attention for their offensive turnaround so far this season — but the raw numbers don’t even tell the whole story. The Mets as a team are second in the National League with a .749 team OPS, behind only the Dodgers, who have a .761 OPS. However, the Mets are leaders in the league with a 115 OPS+, well ahead of the Dodgers and their 111 OPS+ in second place. The difference can be explained by park factors, as Los Angeles’ home stadium, Dodger Stadium, has so far been in the top ten hitter-friendly stadiums of 2022, as has the park of two division rivals: Coors Field and Oracle Park. Meanwhile, in 2022, Citi Field currently sits squarely within the league average for offense.

For Mets fans, OPS+ can also open up an intriguing debate about the best offensive seasons in franchise history.

Not surprising, Mike Piazza holds the Mets franchise record for single-season OPS with a mark of 1,012 in 2000. While impressive, it’s important to remember that 2000 was the MLB high-water mark for offense in modern times, with a League record OPS average of .782.

The 2000 season took place during the height of the steroid era, sandwiched between the 1998 home run chases (Mark McGwire vs Sammy Sosa) and 2001 (Barry Bonds). In this context, the performance of Piazza, while still historic, loses a little of its luster. In fact, his OPS+ this season was 155, which is “only” the sixth best in team history. Mets fans might be surprised to learn that the franchise record belongs to OPS+ Howard Johnson, who posted an OPS+ of 169 in the 1989 season. HoJo’s .928 OPS was nearly 100 points lower than Pizza’s mark, but the league OPS average was a paltry .695 — closer to the previous league average this season with reduced offense. Given the 2022 crime suppression record so far, Pete Alonso’s current OPS of .906 gives an OPS+ of 157, which would push Piazza to sixth on the Mets all-time list.

Some may be surprised to learn that Howard Johnson holds the Mets all-season record for OPS+, a normalized measure of offensive productivity.

While the normalization aspect of OPS+ helps make it a more meaningful stat, it’s not without its limitations. OPS and thus also OPS+ can still be significantly influenced by luck.

A common instance of luck benefitting a batter’s OPS/OPS+ is when a batter makes soft contact but still gets to base through results like an infield single or a pop-up falling in front of an outfielder . Luckily, additional advanced stats can help flag circumstances where OPS+ is being skewed by luck. For example, there are numerous ways to measure the quality of a batsman’s contact, such as: B. the exit velocity.

Balls hit harder generally have a better chance of falling on hits. So if a hitter has a consistently above average exit speed, it’s likely that his high OPS/OPS+ isn’t just a result of luck. Pete Alonso, for example, has an average career exit speed of 91.0 mph, well above the MLB average of 88.4 mph during that time. Unsurprisingly, Pete’s career OPS+ is a robust 140 – a direct result of his penchant for hitting balls very very difficult.

OPS+ is readily available on statistical websites such as Baseball-Reference and is even appearing on stadium scoreboards with increasing frequency. So next time you’re at Citi Field or arguing with an elder about who was the better hitter “back then”, you might have the perfect opportunity to impress your fellows with a detailed explanation of OPS+!

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