Inner Half

Have you ever been watching SportsCenter or listening to a radio host talk baseball and they drop a line like “This guy is on fire! He’s slashing X/Y/Z” or “he’s been awful, only slashing X/Y/Z”? 

If your immediate thought is one of…

1. What the hell does that mean? Or
2. If that’s the case, why haven’t we paid (or released/traded) this guy?

Then this post will be for you. I will explain what a “slash line” is in the game of baseball, what it tells us and why you should (or shouldn’t) trust it.

First, let’s define a slash line and its components. A slash line is a quick summary of a player’s results at the plate. It consists of a player’s batting average, on-base percentage and slugging percentage, formatted like this: AVG/OBP/SLG.

Batting Average (AVG)

Batting average is a player’s total number of hits divided by their at-bats (AB). Simply, how often does a player record a hit?

One of the most basic and well-known statistics in all of baseball, batting average takes on historical value as one of the three statistics in the “Triple Crown” achievement (along with home runs and runs batted in).

Here are the single season records for batting average among players with at least 400 AB:

As you may notice, these records are decades and even over a century old. This is simply a nod to how the game has changed over the years with pitchers becoming more strategic and unpredictable, while also building velocity. The current leader in batting average in 2025 is Aaron Judge, who is batting .339.

There are plenty of issues with relying on batting average to tell the story of a hitter. That’s not to say hitters like Rogers Hornsby and Nap Lojoie weren’t talented, but this is just one number that is influenced by many external factors and needs context.

On-Base Percentage (OBP)

On-base percentage is the amount of times that a player gets on base over his total number of plate appearances. 

Note that we use plate appearances (PA) for OBP and at-bats (AB) for AVG. This distinction is because ABs do not include plate appearances ending in walks (BB), intentional or unintentional, sacrifices or hit-by-pitches (HBP). Therefore, to find a hitter’s OBP, you can follow this formula: 

(Hits + Walks + Hit By Pitches) / (At bats + Walks + Hit By Pitches + Sacrifices)

OBP had largely been ignored throughout the history of baseball, until Billy Beane and Michael Lewis’s book, Moneyball, popularized the number more than ever before. The book opened eyes to such a simple, yet telling statistic: how often a hitter gets on base. After all, a team is more likely to score more runs when there are runners on base. 

Here are the OBP single season records for players with 400+ PAs:

It’s quite unlikely we’ll ever see on-base percentages like the rates from Barry Bonds, Ted Williams and Babe Ruth. Bonds was intentionally walked 120 times in 2004. An elite OBP in current-day MLB is .400, or 40%. The current leader in OBP in 2025 is, again, Aaron Judge with a .447 OBP (he is the only player over a .400 OBP)

Slugging Percentage (SLG)

Slugging percentage tells us the average number of bases per at-bat. When you hear someone say “that guy slugs,” they mean they hit for extra bases effectively. An elite slugger can have a lower AVG but a higher SLG if they hit many home runs or extra base hits. A high-AVG singles hitter will not have as high a SLG as the former.

How is SLG calculated? Basically, the formula weighs the different types of hits differently: a double is worth twice as much as a single, a triple three times as valuable as a single, and a home run four times as valuable as a single. 

It will look like this:

(1B + 2(2B) + 3(3B) + 4(HR)) / AB

Generally the best hitters–that hit for average and for power–will boast the best slug rates, and these are the single season records for SLG (along with their totals for 1B, 2B, 3B and HRs) among those with at least 400 ABs:

It makes sense that players with tons of home runs and extra base hits are going to have huge slug rates. Again, we just don’t see these types of numbers in today’s game because 1) the steroid era has passed and 2) hitting has gotten much harder. You probably guessed it–Aaron Judge is also currently leading the MLB with a .697 SLG, followed by Shohei Ohtani with .614. 

Why slash lines are great data points

Knowing what a player is slashing is very valuable information for front offices. It can easily tell them what kind of hitter they are dealing with. 

If the hitter has a high OBP, they know he gets on base somehow. If the AVG is lower than expected given the strong OBP, they know that this player likely walks a good amount and is disciplined and patient when hitting. If the AVG is average or better than expected, it could be a mix of strengths or more of a batted ball ability. 

A solid SLG will suggest an ability to hit for extra bases, even home runs. A high SLG and low OBP suggests an extremely aggressive power hitter. A low AVG and strong SLG hints at an “all-or-nothing” type of hitter, one that usually strikes out or hits a home run. A high AVG, high OBP and high SLG (like an Aaron Judge) successfully demonstrates who is arguably one of the best hitters in the game. Are you seeing what I’m saying? It’s almost like a sneak peek at a hitter without getting into the nitty gritty. 

Why slash lines fall short

Unfortunately, we can’t put all our eggs into the slash line basket. There are glaring issues with all of these statistics that are worth noting.

The first thing to note is how unreliable batting average can be. As we know, batting average is simple: hits divided by total at-bats. You might think that this is a simple way to realize how prolific someone is at putting the ball in play for hits. The truth is that this number, the batting average, doesn’t tell us what type of hits are being hit. 

Let’s take a hypothetical baseball game and imagine that Player A goes 1 for 4 with a home run and 3 line drive outs, while Player B strikes out 3 times before hitting a ball virtually at his feet and, because he had great foot speed, was able to beat the throw from the catcher to first base. Both Player A and Player B went 1 for 4, and therefore have a .250 batting average. 

Of course Player A and Player B did not have nearly the same quality of game. Player A had the superior game, hitting a home run in addition to 3 hard-hit line drives that unfortunately found a defender’s glove. Player B just eked out a single after striking out 3 times prior. So you see, this is where batting average falls short, it doesn’t take into account the type of hit a batter hits and even though the hitter did everything right, a batted ball can still result in an out–doesn’t sound like something we should keep referencing in debates, huh?

Let’s talk about the issue with on-base and slugging percentage next. Firstly with SLG, the idea to weigh each outcome of a batted ball is really an ingenious one because it allows us to understand who is going to produce at the plate better than his fellow hitters. However, it simplifies things a little too much.

With a single (one base hit) being our “control” value in this case, can we really say that a double is worth 2x what a single would be in a given scenario? Here’s where the nerd in me comes out (thanks Tom Tango) → I was introduced to a concept called “run value” in The Book: Playing the Percentages in Baseball by Tango and others, which, without getting much more into it, discusses how valuable any event (single, double, strikeout, walk, etc.) is based on the base-out situation (by this, how many men on base and how many outs?). I don’t even need to get any more specific for you to know I’m already going here: a double is not 2x a single, a triple is not 3x a single and a home run is not 4x a single and 2x a double. Outside of that, a nit to pick with SLG is that it’s not going to incorporate walks (like AVG) and also isn’t going to give us many more details about a hitter other than his ability to tally bases. 

On-base is a very good statistic and I love to reference it as much as any expert, but it does have the issue of weighting events as equal when they usually are not equal (walks and any hit are equal as you are getting on base all the same, while reaching on an error is apparently not getting on base, despite also getting on base all the same as a walk and a hit).

Fear not! There are ways to improve these great rate stats and I will write another post on a fun one called On-Base PLUS Slug (OPS)–can you guess how it’s calculated?

For the real experts, these statistics also don’t take into account park factors, which is a whole other chapter.

Examples

Before I close this out I want to provide you with a couple examples to prove that you understand this better than others now:

Player A – .260/.360/.500

Player B – .260/.320/.500

So, let’s try this out: Player A’s slash line denotes a batting average of .260, an on-base percentage of .360 and a slugging percentage of .500. Player B’s slash line shows he, like Player A, hits .260, has an OBP of .320 and also equals Player A’s slugging percentage of .500. 

What can we extract from these lines? Well, first thing’s first, both players have a .500 SLG, meaning that they are racking up bases at the same rate, likely hitting home runs and doubles at a good rate each. Player A has an equal AVG (.260 vs .260) and a higher OBP (.360 vs .320) than Player B, suggesting that Player A is more selective with his approach, taking walks more often than Player B, accounting for the heightened rate of getting on base.

Okay, one more. Try it yourself first before reading on: What can we say about Player C versus Player D based on their slash lines?

Player C – .265/.340/.410

Player D – .240/.340/.500

Firstly, let’s write these out: Player C is hitting .265, has an OBP of .340 and slugging .420. Player D is hitting .240 with a .340 OBP and a .500 SLG. 

Player C gets more hits, as is evident by the higher AVG (.265 vs .240), but the hitters still get on base at the same rate (.340 vs .340), telling me that Player D has a bit more plate discipline than Player C. Cool, but Player D’s slug rate is higher than Players C (.500 vs .420)–what can we take away from that? We can say that despite having a lower AVG than Player C, Player D does more damage on his balls batted into play (hitting more extra base hits and home runs) than Player C does, as he may be more of a singles hitter. 

Takeaway

I hope this is beginning to make some sense for the people totally alien to these numbers. It wasn’t too long ago that I was in the same spot, but there’s instances of misleading data points all over baseball and other sports, as well. 

If there’s one thing to take away from reading this whole post, it’s that you can easily get a gauge on how a hitter is producing relative to others with a slash line peek. A great hitter will have strong numbers throughout, but great hitters can present differently.