Baseball 101 is an ongoing series from The Good Phight’s Allie Foster that breaks down some of the multifaceted aspects of baseball for those fans who might not be as familiar with the ins and outs of the game. In this ninth edition, she explains an often-used combination of statistics called a slash line. You can read other entries here.
A slash line is made up of batting average, on base percentage and slugging percentage, in order. Occasionally a fourth slash may be included, that number is on base plus slugging. For the sake of this article we’ll skip discussing OPS.
Batting average is one of the most common stats used in baseball. It’s calculated by dividing a player’s hits by his total at-bats. An at-bat is when the batter reaches base via hit, error or fielder’s choice or is retired on a non-sacrifice. Walks, catcher’s interferences, balks and sacrifice bunts/fly outs/ground outs do not count towards at-bats. The number is calculated to three decimal places, but is said without the decimal. So Realmuto’s .272 average would be read “Realmuto is batting two seventy-two.” The average MLB batting average is currently .247. The highest single season batting average in MLB history was Nap Lajoie, who batted .426 for the Philadelphia Athletics in 1901. Ty Cobb has the highest career average at .366 over an astounding 24 seasons. He had 11,439 at bats over 3,034 games.
On base percentage refers to how often a player reaches base safely including hits, walks and hit-by-pitches. It does not include errors, fielder’s choices or dropped third strikes. Like batting average, it is calculated to three decimal places and is read the same way. The average MLB on base percentage is currently .320. The all-time single season leader is Barry Bonds* at .609 in 2004 and the highest career on base percentage is Ted Williams at .482.
Slugging percentage looks similar to batting average and on base percentage, and is read the same way, but is more complicated to calculate. It only deals with hits, not walks and hit-by-pitches. It’s also weighted, to benefit multi-base hits. The formula for slugging percentage is (1B + 2Bx2 + 3Bx3 + HRx4)/AB. The average MLB slugging percentage is currently .419. The all-time single season leader is Bonds* at .863 in 2001 and the all-time career leader is Babe Ruth at .690.
So what do these numbers mean when put together and why is this such a commonly-used combination?
The problem with only looking at one statistic at a time is that it doesn’t always paint the whole picture. For example, Mike Trout’s current .276 average isn’t exactly turning any heads. His .449 on base percentage, however, is second-best in the Majors. The comparison between his relatively average batting average and high on base percentage implies he’s getting walked a lot. His 49 walks, best in the majors by nine, proves that implication correct.
Josh Bell, on the other hand, is slashing .338/.405/.706. The combination of his high batting average and slugging percentage with only a slightly elevated on-base percentage suggest that he’s hitting often and getting a lot of extra base hits, while not walking a whole lot. His 39 extra base hits are the most in the Majors, confirming that suggestion.
While Christian Yelich has an above-average batting average (.314) and very good on-base percentage (.425), the star of his slash line is his monstrous slugging percentage at .714, second-best in the Majors. This shows that, while he may be getting on base at a decent rate, he’s really excelling at the long-ball. He’s leading the league in home runs with 21.
When a player has high numbers across his entire slash line, like Bell or Cody Bellinger who is slashing .382/.469/.770 and comfortably leads the Majors in all three statistics, it means they are a dangerous offensive threat in every capacity.
So what’s a good slash line to have? It really depends on what type of hitter you’re looking at. For players at the top of the lineup, like Segura, Andrew McCutchen or Bryce Harper, you want to see higher on base percentages. Getting those guys on base in any fashion gives the heart of the order- Realmuto and Rhys Hoskins, who usually have higher slugging percentages- the opportunity to drive them in.
While we’re on the subject of slash lines, can we please just take a moment to marvel at Jean Segura, who is leading the team in batting average, is third in slugging percentage and fifth in on-base percentage? Just last week he was leading the team in all three statistics. It’s so important to have a consistent presence at the top of the lineup and his production is something the Phillies have been missing for a very long time. He’s cooled off a bit lately, but the guy is a hit machine and currently has my vote for team MVP.
*Bonds achieved these during the Steroid Era
All stats are up to date before games on 5/29.