What is an Ace? Definition and Examples
An ace is the undisputed top starting pitcher on a Major League Baseball staff, responsible for anchoring the rotation and facing the opponent's best lineup.
What is an Ace?
An ace is the undisputed top starting pitcher on a Major League Baseball staff, responsible for anchoring the rotation and facing the opponent's best lineup. Historically, an ace was simply the pitcher who started Opening Day or logged the most innings. In modern baseball, the definition has evolved. An ace is a pitcher who consistently combines high strikeout rates with low walk rates, suppresses hard contact, and absorbs innings at an elite level. Every team wants at least one ace to head their rotation, but true aces are rare across the league.
How an Ace is Measured
There is no single formula to designate an ace, but front offices use a specific combination of metrics to qualify one. A modern ace generally posts a K-per-9 above 9.0, a BB-per-9 under 3.0, and an ERA and FIP both under 3.50. Furthermore, an ace must accumulate high volume, typically throwing 170+ innings across 30+ starts. Sabermetric models also look at WAR, where a true frontline starter generally produces at least 4.0 WAR per season. Aces also tend to rank in the top 10 percent of the league in Stuff+ and Pitching+.
Worked Example
Detroit Tigers right-hander Tarik Skubal is a textbook modern ace. During his dominant 2024 season, Skubal posted a 2.39 ERA and an even lower 2.49 FIP over 192 innings. He struck out 228 batters, good for a 10.7 K/9 rate, while walking just 35 batters all season (1.6 BB/9). He led the American League in wins, ERA, and strikeouts, capturing the pitching Triple Crown. His underlying Statcast metrics backed up the traditional numbers, as his fastball and changeup both generated elite Whiff Rate and CSW numbers. When the Tigers needed a stopper, Skubal took the ball.
Why It Matters
Identifying an ace drives massive roster and financial decisions. Front offices build entire pitching staffs around their ace, using them in Game 1 of a playoff series and, if necessary, on short rest in an elimination game. For fantasy baseball managers, drafting an ace in the early rounds provides a stable foundation of strikeouts and ratios. In DFS, aces are the safest high-salary anchors, as their high K-percent guarantees a high fantasy point floor even if they allow a few runs. The presence of an ace elevates the entire team's win expectancy.
Limitations and Common Misceptions
A common misconception is that any pitcher who makes an All-Star team or throws a No-Hitter is an ace. A pitcher can have a fluky half-season of elite run prevention or a single dominant outing without sustaining the workload or strikeout rate required to be a true frontline starter. Another limitation is the term "ace" itself—it is subjective. Some analysts label a pitcher an "ace" based purely on raw stuff, while others demand a track record of multiple seasons of elite ERA+. A pitcher can be an elite reliever or a Closer with ace-level stuff, but the term is strictly reserved for starting pitchers.
Related Terms
In Legends Deck: In Legends Deck, a card with the "Ace" trait designation receives a boost to their base stamina attribute, allowing them to pitch deeper into simulated games. If you slot an ace at the top of your rotation, their high K/9 and low HR/9 ratings suppress the opponent's wOBA and increase your chances of throwing a Shutout.