How does leverage index (LI) influence late-inning clutch hits?

Leverage Index measures the swing potential of a plate appearance relative to an average MLB game state (LI = 1.0). Late-inning plate appearances with runners on base in close games frequently reach LI values above 3.0 to 5.0, meaning each hit has a disproportionate impact on the final outcome.

Why is a runner on second base with one out worth more than 0.6 runs on average?

In empirical MLB historical tracking (RE24), a runner on second with one out yields an average of 0.664 runs before the inning closes, because any base hit to the outfield or multiple consecutive putout advancements provide a strong probability of scoring.

Base-Out Run Expectancy & Win Probability Engine

Q: What is the difference between RE24 and Win Probability Added (WPA)?

RE24 measures run expectancy based strictly on the 24 base-out states (runners on base and number of outs) regardless of score or inning. Win Probability Added (WPA) measures the percentage change in the likelihood of winning the game, directly factoring in inning, run differential, and home-field advantage.

The Mathematics of Clutch Hitting: How Big Hits Shift Win Equity

When Manny Machado steps up with runners on first and second in the bottom of the 7th inning and delivers a shot down the left-field line to extend a Padres lead, the moment feels electric. In modern sabermetrics, that exact electric feeling is quantified through two foundational pillars: Run Expectancy (RE24) and Win Probability Added (WPA).

Rather than relying solely on traditional box score metrics like batting average or raw RBIs, analysts evaluate each plate appearance based on the precise leverage of the game state before and after the ball is struck. A single that breaks a tie in the 9th inning carries vastly different mathematical weight than a single hit with an eight-run cushion in the 3rd inning.

Empirical Run Expectancy Matrix (RE24)

The 24 base-out states represent all possible combinations of runners on base (8 states) and outs recorded (0, 1, or 2 outs). Over millions of major league plate appearances tracked by Retrosheet and MLB Statcast, each state carries an average expected number of runs scored before the end of that half-inning:

Base State	0 Outs	1 Out	2 Outs
Bases Empty	0.481	0.254	0.098
Runner on 1st	0.859	0.509	0.214
Runner on 2nd	1.100	0.664	0.319
Runner on 3rd	1.350	0.950	0.353
Runners on 1st & 2nd	1.437	0.884	0.429
Runners on 1st & 3rd	1.784	1.130	0.478
Runners on 2nd & 3rd	1.964	1.376	0.580
Bases Loaded	2.282	1.520	0.736

Deconstructing the Machado Sequence

In the Padres scenario simulated above:

Starting State: Runners on 1st and 2nd base with 1 out in the bottom of the 7th, holding a 1-run lead (Score: 4-3). The base-out run expectancy is 0.884 runs, and the home team's baseline win probability is 74.2%.
The Batted Ball: A hard-hit line drive pulled down the left field line (104.2 mph exit velocity, 18° launch angle) lands for a double. Both base runners score, and Machado reaches second base safely.
Resulting State: Runner on 2nd base with 1 out, but now holding a 3-run lead (Score: 6-3). The new run expectancy is 0.664 runs, but the two actual runs scored yield an absolute offensive value of 2 + 0.664 - 0.884 = +1.780 RE.
The WPA Surge: The win probability jumps from 74.2% to 88.8%, representing a net +14.6% WPA swing. That single swing effectively seals more than one-seventh of the total game equity.

What is Leverage Index (LI)?

Developed by Tom Tango, Leverage Index measures the volatility of win probability at any given juncture. An average game state has an LI of 1.0. Critical plate appearances—such as tie games late in regulation with runners in scoring position—frequently produce Leverage Indexes above 3.0 to 5.0. When players perform consistently in high-LI situations, they become the linchpins of postseason runs.

Frequently Asked Questions

What is the difference between RE24 and Win Probability Added (WPA)?

RE24 evaluates plays strictly within the context of the half-inning, looking only at the 24 base-out states to estimate how many runs will score before three outs occur. Win Probability Added (WPA) looks at the entire game outcome, evaluating how much closer a team is to winning based on the inning, run margin, home/away status, and outs remaining.

How does launch angle and exit velocity affect extra-base hit probability?

According to MLB Statcast classifications, balls hit with exit velocities above 95 mph qualify as "Hard Hit." Batted balls launched between 10° and 25° are classified as line drives, yielding batting averages over .600 and high extra-base hit conversion rates. Balls hit over 25° become fly balls, which require exit velocities above 100 mph to clear outfield fences for home runs.

Why does the home team have an innate win probability advantage in tie games?

Because the home team bats last (in the bottom half of each inning), they do not need to prevent runs after scoring the go-ahead run in walk-off scenarios. Historically, home teams in MLB win roughly 54% of all regular-season games and hold approximately 58% to 62% win equity in tied 9th-inning situations.