Advanced Baseball Stats Glossary

WAR - Wins Above Replacement

WAR is the single number that attempts to capture a player's total value. It estimates how many additional wins a player contributes compared to a freely available minor league replacement. WAR combines offensive production, defensive value, baserunning, and positional adjustment into one comprehensive metric.

FanGraphs (fWAR) and Baseball Reference (bWAR) calculate WAR slightly differently, particularly in defensive evaluation. For betting purposes, the differences are usually minor - both tell you the same basic story about player value.

Betting Application

WAR is most useful for season-long projections and futures betting. When evaluating team win totals, add up the projected WAR of the roster and compare it to last year. A team that added 8 WAR in free agency is likely undervalued if the win total only moved 3 games. Our prediction methodology weighs these roster changes heavily.

For daily betting, WAR provides context but isn't directly predictive. A 6-WAR player can go 0-4 on any given night. However, when two teams have similar records but vastly different WAR totals, the higher-WAR team is often undervalued - their record probably doesn't reflect their true talent.

wRC+ - Weighted Runs Created Plus

wRC+ is the gold standard for measuring overall offensive production. It takes all offensive events (singles, doubles, walks, home runs, etc.), weights them by their actual run value, and then adjusts for park and league factors. The result is a single number where 100 is exactly league average.

The "plus" adjustment is crucial for betting. A player with a 120 wRC+ at Coors Field is creating 20% more runs than average despite the park inflation. A player with 120 wRC+ at Oracle Park is doing the same despite the pitcher-friendly environment. This allows apples-to-apples comparison.

Betting Application

wRC+ stabilizes faster than batting average, similar to how expected stats stabilize faster than results, making it useful for identifying hot and cold streaks that are real versus lucky. A player hitting .340 with a 115 wRC+ is getting some BABIP luck. A player hitting .280 with a 140 wRC+ is walking a ton and hitting for power - that's sustainable.

For team totals, compare the combined wRC+ of each lineup. A 15-point gap in team wRC+ is significant and often not reflected in the total. Pay special attention when a high-wRC+ team faces a low-strikeout pitcher - contact will be made, and quality contact scores runs.

wOBA - Weighted On-Base Average

wOBA assigns proper weights to each offensive event based on how many runs it actually produces. Unlike OPS, which just adds OBP and SLG together (mixing different scales), wOBA is mathematically coherent. A walk is worth about 0.69 runs. A single is worth about 0.87. A home run is worth about 1.95. These weights are recalculated each year based on run scoring environment.

The scale is designed to look like on-base percentage, making it intuitive. A .320 wOBA is average. A .400 wOBA is elite. But unlike OBP, wOBA properly credits extra-base hits for their additional value.

Betting Application

wOBA is the foundation for expected stats. When you see xwOBA, it's using the same framework but based on quality of contact rather than actual outcomes. The gap between wOBA and xwOBA is pure signal for regression betting.

Team wOBA directly correlates with run scoring. When two teams have similar ERA pitching matchups, look at the wOBA gap between lineups. A .020 wOBA advantage translates to roughly 0.3-0.4 extra runs per game over time.

xwOBA - Expected Weighted On-Base Average

xwOBA takes every batted ball a player has hit, looks at the exit velocity and launch angle, and calculates what the outcome "should" have been based on historical data for similar contact. It strips away luck entirely and shows you the underlying quality of contact.

This is the single most predictive offensive statistic we have. A player's xwOBA is far more stable than their actual results and far more predictive of future performance. When xwOBA and wOBA diverge significantly, regression is coming.

Betting Application

xwOBA is your best friend for player props. The market prices based on recent results. You price based on underlying performance. When a hitter has a .380 xwOBA but only a .320 wOBA (40-point gap), his hit and RBI props are underpriced. He's been crushing the ball but getting unlucky. That changes.

For pitcher props, look at opponent xwOBA instead of batting average. A lineup with a .360 xwOBA but .310 batting average is about to break out. Their hard contact will start falling. Fade the pitcher's strikeout prop.

FIP - Fielding Independent Pitching

FIP measures what a pitcher's ERA "should" be based only on the outcomes they control: strikeouts, walks, hit-by-pitches, and home runs. It ignores what happens when balls are put in play, because research has shown pitchers have very little control over whether a batted ball becomes a hit.

FIP is scaled to look like ERA, so a 3.50 FIP means the pitcher is performing at a 3.50 ERA level regardless of what their actual ERA says. The gap between ERA and FIP reveals luck - good or bad.

Betting Application

When ERA and FIP diverge by more than 0.50, the market is mispricing the pitcher. A 3.20 ERA / 4.10 FIP pitcher has been lucky - his defense has been great, or his BABIP has been unsustainably low. The market sees 3.20 and prices him as an ace. You see 4.10 and fade.

Conversely, a 4.50 ERA / 3.60 FIP pitcher has been unlucky. He's actually pitching like a quality starter but getting burned by bad defense or bad luck. The market undervalues him. You back him at inflated odds.

xFIP - Expected Fielding Independent Pitching

xFIP takes FIP one step further by normalizing home run rate. Instead of using a pitcher's actual home runs allowed, xFIP assumes every pitcher's fly balls will become home runs at the league average rate (typically 10-12%). This removes another element of randomness.

Why does this matter? HR/FB rate is highly volatile year-to-year. A pitcher who gave up fly balls that mostly stayed in the park this year will probably see more leave next year. xFIP predicts this regression.

Betting Application

xFIP is the most predictive pitching metric for betting. It stabilizes faster than ERA and correlates more strongly with future performance. When evaluating a pitching matchup, compare xFIP rather than ERA. The team facing the higher-xFIP pitcher should be favored to score more.

For totals betting, add both starters' xFIP together. Under 7.50 combined? The under has value. Over 9.00 combined? The over has value. This is simplified, but it works as a baseline.

BABIP - Batting Average on Balls In Play

BABIP measures how often batted balls (excluding home runs and strikeouts) fall for hits. League average is consistently around .300. Here's the key insight: while hitters have some control over their BABIP (through speed and quality of contact), pitchers have very little control.

A pitcher with a .250 BABIP has been extremely lucky - only 25% of balls in play against him have become hits. That won't last. A pitcher with a .340 BABIP has been unlucky. Both will regress toward .300 over time.

Betting Application

BABIP is the ultimate regression indicator. When a pitcher's BABIP is 30+ points below league average, their ERA is artificially low. The market prices based on that ERA. You price based on the regression that's coming.

BABIP also explains why some pitchers seem to "lose it" suddenly. Often, they haven't changed at all - their BABIP just normalized. The hits that were finding gloves start finding holes. Same pitcher, different luck.

ISO - Isolated Power

ISO is simply slugging percentage minus batting average. It isolates extra-base hit power by removing singles from the equation. A .250 ISO means the player averages 0.250 extra bases per at-bat from doubles, triples, and home runs alone.

ISO is more stable than home run totals and tells you about raw power independent of batting average. A player can hit .240 with a .280 ISO (power hitter who strikes out a lot) or .300 with a .120 ISO (contact hitter with no pop). Both are useful, but ISO identifies who can change a game with one swing.

Betting Application

ISO is crucial for home run props and totals betting. High-ISO hitters are volatile - they can hit 2 home runs or strike out 4 times. When two high-ISO lineups face each other, the total often has more variance than the market suggests. The over or under can hit by a wide margin.

For player props, ISO helps identify "sneaky power" candidates. A player with .200 ISO but only 12 home runs at the break has been unlucky with fly ball distance. His HR prop for the second half is probably underpriced.

OPS+ - Adjusted On-Base Plus Slugging

OPS+ takes a player's OPS (on-base plus slugging) and adjusts it for park factors and league environment. Like wRC+, it's scaled where 100 is exactly league average. A 120 OPS+ means the player is 20% better than average offensively.

While wRC+ is more mathematically precise, OPS+ is more widely available and tells a similar story. For quick comparisons, they're largely interchangeable - a player with 130 OPS+ and 130 wRC+ is an elite hitter regardless of which metric you prefer.

Betting Application

OPS+ is useful for historical comparisons since it's been calculated retroactively for all of baseball history. When evaluating a player's season-long performance against historical norms, OPS+ provides context. A 150 OPS+ season is rare - only MVP candidates reach that level consistently.

Barrel Rate (Barrel %)

A "barrel" is a batted ball with the ideal combination of exit velocity and launch angle to produce a hit at least 50% of the time with a slugging percentage of 1.500 or higher. Specifically, it requires 98+ mph exit velocity with a launch angle typically between 26-30 degrees (with slightly wider ranges at higher exit velocities).

Barrel rate tells you how often a hitter squares up the ball perfectly. It's one of the most predictive power metrics available and correlates strongly with home run totals, slugging percentage, and ISO.

Betting Application

Barrel rate is highly predictive of future power. A player with 14% barrel rate but only 15 home runs has been unlucky - his barrels aren't all leaving the yard yet. A player with 6% barrel rate and 20 home runs has been lucky - he's hit his home runs on non-barrels that happened to carry.

For totals, high barrel-rate lineups against fly-ball pitchers are dangerous. The ball is going to be hit hard in the air. Some of those will leave.

Hard Hit Rate (Hard Hit %)

Hard hit rate is the percentage of batted balls with an exit velocity of 95+ mph. It's simpler than barrel rate - it just asks "how often does this player hit the ball hard?" without considering launch angle.

Hard hit rate is remarkably stable year-over-year. A player who hits the ball hard will continue hitting the ball hard. This makes it useful for identifying players whose results don't match their underlying contact quality.

Betting Application

Hard hit rate is excellent for totals betting. When both teams feature multiple hitters with 45%+ hard hit rates, runs are likely. Hard-hit balls find holes. They drive in runners. They turn into extra-base hits.

For pitchers, hard hit rate allowed tells you if they're inducing weak contact or getting squared up. A pitcher with low ERA but high hard hit rate allowed is living dangerously - those hard-hit balls will start falling.

CSW% - Called Strikes + Whiffs

CSW% combines called strikes and swinging strikes into one metric that shows how often a pitcher dominates at the plate without the ball being put in play. A high CSW% means hitters are either watching strikes go by or swinging through pitches - both good outcomes for the pitcher.

CSW% stabilizes quickly (around 150 pitches) and correlates strongly with strikeout rate. It's an early-season indicator of whether a pitcher's strikeout gains or losses are real.

Betting Application

CSW% is perfect for early-season evaluation when sample sizes are small. A pitcher with a 35% CSW% but only 8 K/9 through April is about to see those strikeouts spike. The underlying dominance is there - he's just had some bad batted ball luck.

For strikeout props, CSW% is more predictive than actual strikeout rate early in the season. Trust the process over the results.

Exit Velocity

Exit velocity measures how fast the ball comes off the bat. It's the most fundamental Statcast metric and the foundation for expected statistics. Average exit velocity is remarkably stable - if a player averaged 90 mph last year, they'll average close to 90 mph this year.

This stability makes exit velocity the best predictor of future offensive performance. Batting average fluctuates wildly. Exit velocity barely moves.

Betting Application

Exit velocity identifies regression candidates. A player hitting .300 with 87 mph average exit velocity is overperforming - he's not hitting the ball hard enough to sustain that average. A player hitting .240 with 93 mph exit velocity is underperforming - those hard-hit balls will start falling.

Look for the gap between results and exit velocity. That gap is your edge.

Launch Angle

Launch angle measures the vertical angle at which the ball leaves the bat. 0 degrees is a line drive. Negative angles are ground balls. 25-35 degrees is the home run sweet spot. Above 50 degrees is a pop-up.

Launch angle helps explain why some hard-hit balls become home runs while others are ground outs. Exit velocity and launch angle together determine batted ball outcomes.

Betting Application

Launch angle trends reveal mechanical changes. A player who raised his average launch angle from 8 degrees to 15 degrees has likely changed his swing to hit more fly balls. If his exit velocity stayed the same, expect more home runs - he's putting more balls in the air with the same contact quality.

For pitchers, look at launch angle allowed. Ground ball pitchers (low launch angle allowed) keep the ball out of the air. They're safer bets in home run-friendly parks.

Using This Glossary for Betting

These metrics work together. No single stat tells the whole story. Here's a simple morning routine:

1. Check starting pitchers: Compare xFIP (not ERA). Look at BABIP for regression signals. Check CSW% for strikeout potential.

2. Evaluate lineups: Compare team wRC+ or wOBA. Look for xwOBA gaps that signal regression. Check barrel rate and hard hit rate for power upside.

3. Identify edges: When underlying metrics diverge from results, the market is mispricing. That's where value lives.

For deeper dives on specific metrics, see our complete guides:

• xFIP Explained for Betting
• BABIP Regression Guide
• Statcast Metrics Betting Guide
• wOBA Betting Applications
• Expected Stats Guide (xBA, xSLG, xwOBA)
• Barrel Rate and Totals Betting
• Weather Effects on MLB Betting
• Complete Prediction Methodology