From Stuff+ to xERA: The Best Modern Stats for Evaluating Pitchers

ERA and Strikeouts used to be enough to tell the whole story – but not anymore. Advanced metrics are now used to break down pitchers and their performance in a much more granular fashion to dig deep and see what does and doesn’t work on the mound. This article will break down the most insightful modern metrics that help truly understand pitcher performance.

Why Traditional Stats Fall Short

Statistics like ERA and win-loss record have long been the primary metrics by which a pitcher’s performance has been measured. However, these come with significant flaws on their own. ERA is often influenced by factors outside of the pitcher’s control - including defensive performance, official scorer decisions, and plain old luck. Without further context, the win-loss record is maybe the most misleading stat in baseball. Even strikeouts and walks, while important – leave out critical elements to understanding performance, including contact quality, pitch deception, and sequencing.

The Rise of Advanced Pitching Metrics

Technological advances in stat tracking have fueled a data revolution for the sport. First introduced in 2015, Statcast is Major League Baseball’s advanced tracking system and measures nearly every movement on the field.

Hawk-Eye is the camera-based tracking system that replaced parts of the original Statcast hardware in 2020. It uses 12 high-speed cameras that are installed in various regions of each stadium to track everything from player positioning to batted ball trajectories, pitch location, and ball spin. This has allowed teams and analysts to focus more on underlying skill and not just results.

 Key Modern Metrics You Need to Know

1.     Stuff+

Stuff+ quantifies the quality of a pitcher’s raw tools. It factors in things like velocity, pitch movement, release point, and spin rate. The metric itself is measured on an even playing field where the league average is 100 and any number above 100 is above league average and vice versa. This can be a great metric to identify pitchers with elite tools regardless of whether results have caught up yet.

2.     Pitching+

Pitching+ combines Stuff+ with Command+ and incorporates how well a pitcher locates their pitches within the strike zone. This helps distinguish throwers from refined pitchers. A veteran pitcher whose velocity has started to decline but who locates well, can still have a strong Pitching+ number.

3.     xERA (Expected ERA)

This is a statcast-based metric which estimates what a pitcher’s ERA should be, based on quality of contact, strikeouts, and walks. This is another metric focused less on results and more on expected results.

4.     FIP (Fielding Independent Pitching)

FIP is a metric that focuses on the things a pitcher can control – namely strikeouts, walks, and home runs. It is helpful because it removes defensive performance and luck from the equation. Although this is a very simple metric, it is a powerful one for isolating pitcher performance.

5.     K-BB% (Strikeout Minus Walk Rate)

By simply subtracting the walk rate from the strikeout rate you get another stat considering the two main things within a pitcher’s control – strikeouts and walks. Like FIP, it is a defense-independent stat and a strong predictor of strikeout ability and control.

6.     SwStr% (Swinging Strike Rate)

Simply the percentage of pitches thrown where the hitter swings and misses. It is a great illustration of “stuff” and is often seen as an early indicator for breakout pitchers.

7.     CSW (Called Strikes + Whiff Percentage)

This metric combines called strikes and whiffs to illustrate the overall ability for a pitcher to generate strikes. It is great for evaluating pitch quality and sequencing.

How to Use These Metrics Together

Although these are powerful metrics used to evaluate a pitcher’s performance, no single stat tells the entire story – context matters. So, let’s take a look at several of these for Paul Skenes’ 2025 season to date:

·      Stuff+: 108 – Above Average

·      Pitching+: 115 - Excellent

·      xERA: 2.46 -Elite

·      FIP: 2.49 – Elite

·      K-BB%: 21.1% - Elite

·      SwStr%: 13.7% - Very Good

·      CSW%: 28.5% - Very Good

By looking at these metrics alongside one another, you can get a much better idea of the skill a pitcher possesses and what future performance may look like.

Closing Thoughts

Modern stats let us look beyond ERA and win-loss records to really get a good idea of the skill level behind pitchers, looking primarily at things within their control. Understanding these tools can make you a sharper fan and analyst – whether you’re looking for an edge in your fantasy baseball league or an edge at the sportsbook, you can start to gain a leg-up over the competition and line-setters. So next time SportsCenter shows you a pitcher’s ERA or win-loss record – remember to take it with a grain of salt and do some of your own research. Dig deeper.