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Making An Ace, Part 1: Defining An Ace

Where do the so-called “aces” in the MLB come from? How did they get there? Let’s find out.

Arizona Diamondbacks Photo Day Photo by Christian Petersen/Getty Images

This is the first part of a series that I am calling “Making An Ace”. We are going to look at these so-called aces and learn from them. Do they have traits in common? Where did they come from? How were they developed? And so on. Today’s focus will be simple: to define what an “ace” actually is.

Top of the rotation pitchers, also known as “aces” (at least by some people, we’ll get to that), are one of the hardest-to-get commodities in baseball. Per Spotrac, a wonderful website full of professional sports salary information, starting pitching makes up the highest total of money spent in the MLB at a whopping 57.7% of all MLB spending for players. That leaves the remaining 42% for every other position on the field.

This is product of both value and rarity. Pitchers, as a whole, are only assigned 43% of the total WAR in a season, with about 350 of that WAR going to starting pitching and the other 80 or so WAR going to relievers (however, this is shifting from starters to relievers the last few seasons). A standard baseball roster has 5 starting pitchers and at 30 teams, that’s about 150 starting pitchers at any given time (there are always more under contract due to injuries and what not, but we’re keeping it simple here). That averages out to about 2.3 WAR on average per starting pitcher.

  • Relievers average about 0.333 WAR per player (assuming 8 relievers on a team)
  • Position players average about 1.58 WAR per player (assuming 12 position players)

Again, these are simplified examples, but it clearly shows that starting pitching is the most valuable spot on the field. But it’s not just the value on the field that makes them such a commodity - pitchers are notoriously known for having very volatile careers, both because of performance ups and downs and a much greater injury risk than position players. In fact, pitchers are so volatile, that a massive study examining the average career length of MLB players purposefully left out pitchers.

So, to summarize, not only are starting pitchers the most valuable position on the field, they are also the most volatile position. That means obtaining quality starting pitching, especially for any lengthy period of time, can be extremely difficult. And as such, they are paid far more than any position on the field.

But first, we need to define what an “ace” actually is. The term is used very broadly among baseball fans and analysts but its definition is rather loose.

The simplest definition, and the one that is used on Wikipedia, is as follows:

In baseball, an ace is the best starting pitcher on a team and nearly always the first pitcher in the team’s starting rotation.

This means that each team has one ace and that is it. However, despite the simplicity, is that the most common definition of an ace?

The MLB website actually has “ace” as a glossary term. And while it aligns with the Wikipedia definition, it also includes:

though [ace] can also be used to describe an elite pitcher in general. Therefore, a team with multiple elite pitchers is said to have more than one ace.

This seems to be the more common usage of the term “ace”, at least in my experience. Many fans seems to relate “ace” to quality of pitching rather than simply being the best pitcher on a given pitching staff. I sent an e-mail out to the AZ Snake Pit staff and Jack Sommers gave his definition:

Qualified for ERA title (Min 1 IP per each team game played) and an ERA+ over 120, and over multiple seasons, (although not necessarily EVERY year......stuff happens). This threshold may not seem all that high to some, but please consider the following three points:

1.) There are usually about 20-21 such pitchers on average per year reaching ERA Title Qualified and 120 ERA+. Right now there are 35, but as season goes on a dozen or so of those guys will fall by the wayside through either injury or lesser performance or both. Report Link 1

Important to note that this number has held fairly steady the last 9 years, despite the massive drop in guys that throw 190-200 IP per year. This means that front end guys remain about the same, but teams are less likely to run back end innings eaters with mediocre run prevention out there for quite so many innings any more.

2.) There are only 9 pitchers that have managed 4 or more such seasons over the last 9 years. Report Link 2

3.) There are only 3 pitchers that have reached that threshold each of the last 3 seasons, (including 2019) Verlander, Scherzer, and Greinke.

However there are 18 pitchers who have reached that threshold in at least 2 of the last 3 seasons. Report Link 3

So I would say that there are approximately 15-20 “ACES” per year capable or likely to give you both innings and run prevention at such a level in any given year. But outside of a handful of guys, they are very difficult to count on year in year out because injury is such a disrupter.

While you may not agree precisely with the exact numbers that Jack used, that seems to be a very excellent, yet simple, set of requirements to be an ace:

  • Qualified for the ERA title (1 IP per team game)
  • ERA+ of 120 (~20% better than average)
  • Sustained over multiple years, though not necessarily consecutively

What’s also useful about this methodology is that this naturally tends to limit the number of aces at a given time.

So this gives us about three options so far, albeit there are certainly other possibilities. However, these seem to be the three most common, so it’s time for a poll!


How would you define an "ace"?

This poll is closed

  • 7%
    The best pitcher on each team (30 aces)
    (5 votes)
  • 85%
    The BEST pitchers in baseball, regardless of position in rotation (e.g. qualified for ERA title, 120 ERA+, etc., generally 15-25 aces at a given time)
    (58 votes)
  • 2%
    Both the best pitcher on each team and the best remaining pitchers in baseball (30-50 aces)
    (2 votes)
  • 4%
    Other (please define in comments)
    (3 votes)
68 votes total Vote Now

Based off this information, I will return with Part 2 of Making An Ace and select our sample pool of “aces” to evaluate.