We move on from batting average to discuss a much simpler statistic, as well as a weighted version of batting average. These two new statistics, along with batting average, have over the last decade come to comprise the base-level portfolio of a batter’s hitting abilities.
On Base Percentage
Conceptually, this is the simplest rate statistic for a hitter. It is the number of times a runner gets on base per plate appearance, although we do still remove sacrifice hits since that is typically a managerial decision. As an equation:
\text{OBP} = \dfrac{\text{H} + \text{BB} + \text{HBP}}{\text{PA}-\text{SH}}We’re adding every way a hitter can reach base without defensive errors — hits, walks (BB, which is short for “Base on Balls”), and hit-by-pitches — and dividing by their plate appearances, minus any sacrifice hits.
OBP came into the cultural consciousness with Moneyball back in the early 2000s, although a great Foolish Baseball video discusses how Earl Weaver of the Baltimore Orioles quietly did something quite similar several decades earlier. Regardless, the idea is simple: rather than valuing just hits very highly (hits are cool!), we should instead value not getting out. If you’re not amazing at hitting, but you’re still able to get a lot of walks through excellent plate discipline, you should be rewarded to some extent.
Perhaps the weirdest example of this was Juan Soto from this year, who only had a .242 batting average, but his OBP was .401. Despite only getting a hit less than a quarter of his at-bats, he still got on base just over 40% of the time. That’s an important element of his game!
In general, I’d say .400 is the baseline for a very good OBP.
Slugging Percentage
You may know that a slugger is someone who hits the ball really hard, often for extra bases or home runs. As such, the slugging percentage (SLG) is a weighted batting average where instead of measuring total hits per at-bat, we measure total bases per at-bat.1The careful reader may note that this means it’s not a “percentage” in any meaningful way. It’s certainly mathematically possible for someone’s slugging percentage to be above 1. It’s more accurately a “slugging rate”.
To break it down among singles, doubles, triples, and home runs (1B, 2B, 3B, HR respectively), we get this equation:
\text{SLG} = \dfrac{1\cdot\text{1B} + 2\cdot\text{2B} + 3\cdot\text{3B} + 4\cdot\text{HR}}{\text{AB}}However, it’s simpler to think of it as “total bases per at-bat”. So, someone with a .500 SLG gets, on average, half a base per at-bat, which would be quite good.
Here are a few fun statistics for OBP and SLG. We’ll only be considering the Live Ball Era, which began in 1920.2This is when Babe Ruth discovered that home runs are pretty fun to hit, and players largely stopped treating baseball like a game of cricket.
- The highest season OBP by a qualified player with a BA less than .300 was Mark McGwire in 1998, who had a .299 BA and a .470 OBP. (When you hit 70 home runs, a new MLB record at the time, you’ll get walked a lot.) 3As a final note, it’s always funny to me how home runs are included in OBP. Of course it would be silly to not, but the name makes it a bit confusing. You don’t get on base with a home run. Maybe it should be the “Avoiding Outs Percentage” instead.
- The lowest season OBP by a qualified player with a BA greater than .300 was Shawon Dunston in 1997. He had a .300 BA on the dot, yet only eked out a .312 OBP. He struck out 75 times, and only walked 8 times. That’s pretty abysmal.
- The highest season SLG by a team that won the World Series was the 1927 Yankees, with a .488 SLG.
Continue to Day 3 – OPS and OPS+
- 1The careful reader may note that this means it’s not a “percentage” in any meaningful way. It’s certainly mathematically possible for someone’s slugging percentage to be above 1. It’s more accurately a “slugging rate”.
- 2This is when Babe Ruth discovered that home runs are pretty fun to hit, and players largely stopped treating baseball like a game of cricket.
- 3As a final note, it’s always funny to me how home runs are included in OBP. Of course it would be silly to not, but the name makes it a bit confusing. You don’t get on base with a home run. Maybe it should be the “Avoiding Outs Percentage” instead.