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What is On-Base Percentage?

Overview

The name of the game in baseball is scoring runs. Simply put, the more often a team gets runners on base, the higher the chance it can score more runs. While hits are important, getting hits is only one method of getting on base.

Hitters can also reach base by drawing walks and getting hit by pitches. Both of these are very important in how to accurately assess a hitter’s offensive production. Understanding all these factors of getting on base led to the creation of On Base Percentage, or OBP, as a traditional stat used to measure how often a hitter gets on base.


OBP Explained

Let’s take two hitters for instance, Player A has a .250 batting average and Player B has a .300 batting average, in 100 at-bats. Which hitter do you think is a better offensive player? Now imagine Player A has 25 walks to go along with their 25 hits, while Player B has 10 walks to go along with their 30 hits.

This means that Player A recorded a .500 OBP to Player B’s .400, with all else being equal. Player A has a higher On-Base Percentage than Player B who had a much higher batting average, which means Player A is arguably more valuable as a total offensive player. This is the main idea behind why it’s so important to understand On-Base Percentage.

When we’re analyzing a hitter, we don’t just want to know how good they are at getting hits, we want to know how good they are at being an offensive run producer. This includes measuring outcomes such as walks and hit-by-pitches, in addition to batting average.

In practice, On-Base Percentage is calculated using the following:

OBP = (Hits + Walks + Hit by Pitch) / (At Bats + Walks + Hit by Pitch + Sacrifice Flies)

On-Base Percentage is a rough measure of how many times a hitter reaches base compared to their total number of plate appearances. While OBP is widely considered a superior metric to batting average, it too is not without flaws. 

While it does account for more outcomes, similarly to batting average, it weighs hits and walks the same; when we know that certain hit types like home runs are more valuable than others.

In a typical MLB season, the league average OBP is around .330. A well-above-average hitter tends to have an OBP between .350 and .380, while the best hitters may have OBPs over .400.

Summary

On-Base Percentage is one of the first metrics that help us understand how important it is to consider outcomes outside of just getting hits, and leads us to start utilizing more advanced offensive statistics to grasp a player’s entire offensive contribution.


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