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Why does ‘K’ stand for ‘strikeout’ in baseball?

It’s around the 7th inning and the home team pitcher is throwing fire. He’s up to 9 strikeouts already and the other team can’t figure him out!

In the outfield, fans are turning over ‘K’ signs each time the hurler scores another strikeout.

But where does the letter ‘K’ come from and why does ‘K’ mean strikeout in baseball? Let’s find out.

What happens when a player strikes out?

One of the first lessons you learn in baseball, even if you have very little knowledge about the game, is the classic rule of “three strikes and you’re out!”

That’s exactly what happens when a player strikes out.

A strike occurs when the batter swings and misses a pitch or doesn’t swing at a pitch in the strike zone.

why K means strikeout in baseball

The strike zone spans horizontally across the plate and vertically from the player’s knees to just below the shoulders. Sometimes, they’ll call this the “letters of the chest”, meaning the team name or logo on the uniform shirt.

If you hit the ball and it lands in foul territory, this also counts as a strike. However, you cannot get a third strike for a strikeout on a foul ball.

When the pitcher strikes out the batter, it’s recorded as an out and a new batter must come to the plate. The strikeout is registered as a ‘K’ in the scorecard.

Why ‘K’ means strikeout in baseball?

The reason we use ‘K’ to note a strikeout has its origins in the very beginning of baseball history.

In 1859, Henry Chadwick developed a scoring system for baseball. Interestingly, Abner Doubleday, credited as the creator of baseball, developed the game 20 years earlier.

This means there were two decades of baseball with no proper scorekeeping!

When Chadwick began developing his scorekeeping system, he had already used the letter ‘S’ to mark a hitter recording a single. So, he needed a new letter for strikeout.

Historians best guess is that Chadwick used ‘K’ because it was the last letter in the word “struck”.

Since then, using the letter ‘K’ has become the go-to method for scorekeepers and baseball fans.

Why does ‘K’ mean strikeout in baseball instead of ‘SO’?

A lot of people wonder why Chadwick chose ‘K’ over ‘SO’. The latter makes more sense to many people because ‘S’ stands for strike and ‘O’ for out.

‘SO’ is used to represent strikeouts when you look at the final box score or a player’s individual stats. So, both abbreviations are used today in different ways.

That leaves the question: why did Chadwick opt to use ‘K’ and why do we still use it today?

In Chadwick’s time, the term “strikeout” wasn’t really used. It probably never even occurred to him to use it in his scoring system. The popular term at the time was “struck”. Chadwick used this term to land on ‘K’.

What does a backwards ‘K’ mean in baseball?

If you look at a baseball scorecard or happen to notice fans holding ‘K’ signs in the stands, you may notice the appearance of a backwards ‘K’.

This is not a typo or mistake. A backwards ‘K’ expresses that the batter struck out looking, meaning they didn’t swing the bat for the final strike.

The backwards ‘K’ is a relatively new trend that has its roots in the 1980’s New York Mets and the legendary Dwight “Dr. K” Gooden.

How rare is a strikeout in baseball?

How hard is it for a pitcher to get a ‘K’ really depends on several factors. The most significant of these factors is the pitcher’s own skill, ability and style.

Naturally, a great pitcher (like “Dr. K”) is going to record strikeouts more regularly than a player that is struggling on the mound.

You also have to consider the opposing team’s batting skill. Good hitters will strike out less than bad ones. If a pitcher is facing an all-star lineup of batters, it will be harder for them to record ‘Ks’.

That said, the best way to estimate how often a pitcher will throw a strikeout is “K rate”. This is a simple measure that calculates how often a pitcher strikes out a batter.

K rate = Total strikeouts ÷ Total batters faced

So, if a pitcher had 100 strikeouts after facing 1,000 batters, they’d have a .100 K rate, or 1 strikeout for every 10 batters.

Are strikeouts the best way to tell if a pitcher is good?

Baseball is full of stats and various metrics that we use to evaluate the quality of a player. For pitchers, strikeouts is one of the first stats that fans like to check.

strikeouts in pitcher's stats

Strikeouts are electric to watch and they can reflect the dominance of a pitcher. However, they don’t always tell the full story, which means they aren’t the best measure of a pitcher’s quality.

You can have a phenomenal pitcher that doesn’t record many strikeouts because that isn’t their approach.

For example, a ground ball pitcher is a term used for a player that pitches with the intent to get the batter to hit ground balls. It’s easy for the infield to field these balls and record the outs.

Thus, a better stat to use is earned run average, or ERA. This shows how many runs a pitcher will allow in a 9-inning game. It helps you see how efficient a pitcher is at recording outs, whether by strikeouts or other means.

Who has the most strikeouts in baseball?

Now that we’ve discussed the history of why the letter ‘K’ is used to represent strikeouts in baseball, let’s look at some fun records and statistics regarding strikeouts.

Currently, Roger Clemens, Kerry Wood and Max Scherzer tie for the record for the most strikeouts in a 9-inning game with a whopping 20. This means only 7 outs were recorded without a strikeout in these games!

Tom Cheney was able to strike out 21 batters in a game, but over 16 innings.

Nolan Ryan holds the record for most strikeouts in a career. In 26 seasons, he notched an incredible 5,714 ‘Ks’. That’s almost 1,000 more than the next closest player, Randy Johnson (4,875).


The best (and most baseball) explanation of why ‘K’ means strikeout in baseball is because that’s the way it’s always been. So, why change it?

Henry Chadwick, the father of baseball scorekeeping, used the letter ‘K’ because it was the last letter in the word “struck”, which was the common term for a strikeout at the time.

And, the ‘K’ stuck for centuries of baseball history to come.