As time goes on, more baseball fans are discovering just how important on base percentage (obp) is when evaluating the offensive performance of a major league baseball player.

After all, batting average is a limited metric. Despite its historical importance and tradition, its greatest limitation is that it leaves walks out of its equation.

But assuming you’ve realized the importance of obp, one ultimately comes to the question, “What is a good on base percentage?”

Most of us have a vague idea. .400 is excellent. .350 is solid. .300 or less is not so good.

Before we answer this question definitively, let’s remind ourselves why on base percentage is so important in baseball to begin with.

Why On Base Percentage Beats Batting Average

A naysayer could question why baseball suddenly prefers obp to batting average when evaluating a hitter. After all, the person is called “a hitter” - aren’t hits really what matter?

Well… no. Hits are great. Hits are important. Hits are, to be fair, even better than walks.

But not that much better.

After all, what is the most important job of any baseball player at the plate? It’s not to get a hit. Rather, the most important job of any batter is to not make an out.

In other words, it’s to reach base. After all, when a hitter reaches base, it often means nobody on the field has made an out. 

Why is not making an out so important? Why is it even more crucial that the batter reaches base getting a hit or even driving in a run?

To answer this, think back to your old economics classes. I know you likely don’t want to think back to them, because same here, but hear me out.

One of the major drivers of an item’s value is the scarcity of a resource. When there is a lot of demand for an item, and the item is scarce, the price goes way up. 

Because everyone wants it. They’re willing to pay top dollar for it. Scarcity is crucial. Well, scarcity is also crucial in baseball.

What is one of the most scarce resources in a ballgame?

Outs.

Because a team only gets 27 outs. And at the end of 27 outs, you have no more chances to score. Which means if you are behind in the scoring, you lose.

And losing is bad. Therefore, it is important not to make outs. Every single time a hitter does not make an out, it increases the chances that their team will score a run or multiple runs.

And scoring more runs than your opponent is the ultimate goal of the game. Of course, a hit helps you score runs. But so does a walk. Because when you walk, you’re not making an out and you are preserving your scarce resource.

On base percentage is better than batting average because it better accounts for this scarce resource and the most important job of a hitter at the plate - not making an out.
 

How Is On Base Percentage Calculated?

On base percentage is a relatively simple formula - though more complicated than batting average. The numerator consists of the ways that a player can get on base that don’t contribute to creating outs:

Hits + Walks + Hit by Pitch

The third element may surprise you but it’s perfectly sensible. When a batter gets hit by a pitch a) It hurts and b) that batter gets on base without creating an out. Thus, it goes to help boost their on base percentage.

So there’s the numerator. What about the denominator?  There are four elements that are included here:

At Bats + Walks + Hit By Pitch + Sacrifice Flies

At bats is an essential element here just as it is in calculating batting average. But what matters here is the total amount of times a player comes to the plate and either a) makes an out or b) does not make an out.

If a player gets a hit or takes a walk, that player does not make an out. And now we know the same is true with a hit by pitch. 

Now, we know if the batter is tagged out or the throw beats the batter to first base, that player makes an out, which is bad. But what about sacrifice flies?

After all, the batter is out on a sacrifice fly but another baserunner advances or perhaps even scores a run? Shouldn’t this be seen as a net positive?

Nope. Remember, the scarce resource is outs, not runs. You can score unlimited runs. You only get 27 outs in which to do it.

Not making an out is the most important thing, but sacrifice flies are outs. So, they are a net negative and count against you in the formula.

All in all, the on base percentage formula works as such:

OBP =               hits + walks + hit by pitch
                        ________________________
             at bats + walks + hit by pitch + sacrifice flies

There are technically other elements to consider like a fielder’s choice and sacrifice bunts. But remember, these are in effect just outs. They use up your scarce resource.

So What Is a Good On Base Percentage?

In a way, quantifying a good on base percentage is straightforward. You start with the league average on base percentage, and evaluate particular batting averages against it.

The more you deviate from the league average in a positive way, the better your on base percentage.

In 2018, the league average OBP was .318. So far in 2019 it’s hovering around .322. So let’s say that, lately, the average OBP is roughly .320.

Now, on base percentage tends to run about sixty points higher than batting average. So if the average obp is .320, the league average BA would be around .260.

This intuitively feels right. If a .260 batting average is the league average then a batting average of .280 is pretty solid, .300 is very good, and significantly higher than .300 is great.

If we add 60 points, then a .340 OBP is solid, a .360 is very good, and significantly higher than .360 is great, with an on base percentage of .400 or higher being generally exceptional.

Since last year (2018), the top 5 players in OBP are the following:

Mike Trout - .465
Mookie Betts - .427
Christian Yelich - .412
Joey Votto - .407
J.D. Martinez - .405.

Out of those five, four of them also have a slugging percentage above .600 - Votto being the exception. These are clearly elite level hitters. It’s also interesting to note that all but Votto have a batting average above .300 as well.

And here are your 5 worst players in terms of on base percentage since last year:

135. Evan Longoria - .275
136. Salvador Perez - .274
137. Kyle Seager - .273
138. Kevin Pillar - .272
139. Chris Davis - .243

Chris Davis. Oof. That would put his expected batting average around .183. In reality it’s .167. Even worse.

And here’s your list of top 5 all time on base percentage leaders:

Ted Williams - .482
Babe Ruth - .474
John McGraw - .466
Billy Hamilton - .455
Lou Gherig - .447

The legendary Williams of the Boston Red Sox beats both Babe Ruth and Barry Bonds, who, by the way, came in sixth at .444 and is also known to have hit a home run now and again.

The Hall of Fame clearly respects OBP.  And so should you.