RE Added and WPA: The Two Stats That Finally Measure What Actually Happened

Traditional baseball stats describe what happened. These two tell you what it meant.

Win Probability Added (WPA) and Runs Expectancy Added (RE Added) are not incremental improvements on batting average and ERA. They are a different kind of accounting entirely — one that weights every plate appearance by the situation it occurred in. Together, they give us the first real answer to two questions baseball has always struggled with: who actually came through when it mattered, and who quietly made the game easier to win without the box score knowing it?

WPA: The Only True Measure of Clutch

Win Probability Added is unique in baseball statistics because it is not a proxy for clutch performance. It is clutch performance, defined precisely and applied to every plate appearance in the game.

Here is how it works: before every at-bat, both teams have a calculable win probability derived from the score, inning, outs, and base state — built from decades of historical game data. When the at-bat ends, that probability shifts. The difference is WPA. A positive number means the batter helped his team win. A negative number means he hurt them. For pitchers, we calculate WPA as the sum of the changes in win probability for every half inning that he pitches in, calculated as the difference between his team's win probability after the last pitch he throws and before the first pitch he throws. There is no ambiguity, no adjustment, no estimate. Every PA in baseball history has a before and an after.

This makes WPA the only stat in baseball that automatically accounts for context. Consider two plate appearances:

A batter comes up in the bottom of the fifth inning, his team trailing by one, runners on second and third, two outs. He hits a two-run single. His team's win probability jumps from roughly 40% to 72%. That is +0.33 WPA — a massive contribution.

Now consider a batter who hits a grand slam with no outs in the top of the eighth of a game his team leads 8-0. Four runs score. The crowd goes wild. But his team's win probability barely moves — they were already at 99%. His WPA for that grand slam: +0.01.

Traditional stats see the grand slam as the more impressive play. WPA knows better. The two-run single in a tight game changed the outcome of the contest. The grand slam changed the final score.

This is why WPA is the purest available measure of clutch: it does not care about the optics of a moment. It does not reward volume in low-leverage situations. A player who consistently produces when the game is genuinely in doubt accumulates WPA at a rate no traditional stat can capture. A player who pads his numbers in blowouts will look good in the box score and flat in WPA.

RE Added: Credit for What the Box Score Ignores

While WPA captures the win-or-lose impact of a plate appearance, Runs Expectancy Added measures something different: how much a player changed the run environment within the half-inning, regardless of what eventually happened.

Every combination of outs and baserunners has a historical average number of runs that score before the inning ends. These averages — built from thousands of innings of MLB data — form the runs expectancy matrix:

RE Added for any plate appearance is:

RE Added = (RE when you entered) + (actual runs that scored) − (RE when you left)

A positive number means the batter increased run expectancy, while a negative number means he decreased it.

Where RE Added earns its keep most is on plays that never show up in the traditional box score. A batter grounds to second with a runner on first and no outs — on the surface, just an out. But if that ground ball moved the runner from second to third, the run expectancy just shifted. RE Added sees it. A fly ball that advances a runner from second to third gives the batter no official credit in standard stats, but RE Added knows that a runner advanced and the out was the cost of doing business. These are the plays that teams value internally and that the public stats have always flattened to zero.

A Tale of Two Pitchers: May 30, DET @ CWS

The top of the sixth inning on May 30 is a perfect case study for both metrics working simultaneously.

Anthony Kay started the sixth with a clean slate — bases empty, no outs, 0.498 expected runs. He proceeded to allow two baserunners ultimately leaving with runners on first and second with nobody out. Run expectancy at that moment: 1.573. His team's win probability had dropped sharply.

Grant Taylor entered that mess and retired the side without allowing a run.

Kay's RE Added: −1.075. He took a situation worth 0.498 expected runs and turned it into one worth 1.573 — more than a full run of damage created before leaving the field. His team's win probability fell in step with every baserunner he allowed.

Taylor's RE Added: +1.573. He absorbed a bases-outs situation worth nearly 1.6 expected runs and zeroed it out. His WPA reflects the same truth: entering a high-leverage situation and retiring the side in order is one of the most impactful things a relief pitcher can do, and WPA assigns the credit directly to him for it.

Why ERA Gets Both of These Wrong

ERA is built on a simple assumption that breaks in two different ways when a starter and reliever share a half-inning.

Under traditional ERA rules, the two inherited runners Kay put on base are charged to Kay — but only if Taylor lets them score. If Taylor escapes the jam, Kay gets charged zero runs. If Taylor surrenders both, Kay takes the hit for runners he put on.

This means Kay's ERA outcome depends entirely on what Taylor does after Kay has left the building. And Taylor, no matter how heroic his escape, shows ERA: 0.00 — indistinguishable from a reliever who entered with bases empty and retired the side in order.

2026 Leaderboards (Through June 13)

The comparison across leaderboards is itself informative. Yordan Alvarez leads RE Added by a comfortable margin but doesn't crack the WPA top five — his run production has been exceptional but concentrated in situations where the game's outcome was already leaning one way. Nathaniel Lowe flips that: he leads the WPA list but doesn't appear in RE Added's top five, suggesting his contributions have been especially timely rather than high-volume. Nick Kurtz ranks fourth in RE Added and second in WPA, one of the few batters who scores well on both dimensions — consistent production that also tends to arrive when it matters. Yandy Díaz sits second in RE Added and third in WPA, similarly coherent across both lists.

On the pitching side, Shohei Ohtani leads RE Added and ranks second in WPA — dominant by either measure. Jacob Misiorowski is second in RE Added but absent from the WPA top five, a sign that his run prevention has come in games that were already well in hand. Davis Martin leads the WPA list despite not appearing in RE Added's top five, meaning his strongest outings have come in tight games where each out carried maximum weight. A starter who throws seven shutout innings in a 1-0 win accumulates more WPA than one who does the same in a 9-0 blowout, even if their RE Added numbers are identical — and that gap is exactly what separates Martin from some of the higher-volume names above him.

The Bottom Line

RE Added treats every plate appearance as its own accounting entry, charging or crediting each player for the change in run expectancy they produced — regardless of what happened before they arrived or after they left. WPA does the same, but denominated in win probability instead of runs.

They answer different questions. RE Added asks: how much did you change the run environment? WPA asks: how much did you change the odds of winning? Used together, they tell a fuller story than either could alone — one that ERA, batting average, and RBI have never been able to tell.

You can explore full leaderboards for both stats on our MLB stats pages.