MLB Betting Glossary — Every Baseball Wagering Term Explained
Available in US
Baseball has its own language, and betting on baseball adds another layer of vocabulary on top. When I started wagering on MLB from the UK, I kept a running list of terms I did not understand — by the end of my first season, the list had over sixty entries. Some were baseball-specific (bullpen, innings, at-bat), some were betting-specific (dime line, juice, listed pitcher), and some sat at the intersection of both. The UK is the third-largest gambling market in the world at 27 billion dollars, and UK bettors are sophisticated — but the American terminology can still be a barrier when you first encounter it.
This glossary covers the terms you will encounter when betting on MLB from a UK sportsbook. It is written for bettors, not baseball historians, so the definitions focus on how each term affects your wager rather than its broader context in the sport. Andrew Rhodes, CEO of the UK Gambling Commission, has spoken about international regulators working together on shared standards — and as MLB betting grows globally, a common understanding of the terminology is part of that foundation.
Table of Contents
Terms A to L
Action bet. A bet that remains live regardless of pitching changes before the game. If the listed starter is scratched, your bet stands at adjusted odds. Contrast with listed pitcher bet.
At-bat. A single plate appearance by a batter, excluding walks, hit-by-pitches, and sacrifices. Relevant to hit-total props.
Bullpen. The group of relief pitchers available to a team after the starting pitcher is removed. Bullpen quality affects late-game outcomes and is a key factor in full-game versus F5 analysis.
Closing line value (CLV). The difference between the odds you bet and the final odds at game time. Consistently beating the closing line is the strongest indicator of long-term profitable betting.
Dime line. A moneyline where the spread between the favourite and underdog is 10 cents in American odds — for example, -130/+120. Translates to roughly 2% margin, making MLB moneylines among the most bettor-friendly markets in sport.
ERA (earned run average). The average number of earned runs a pitcher allows per nine innings. Widely cited but less predictive than advanced metrics like xERA for betting purposes.
F5 (first five innings). A market that settles based on the score after five complete innings. Isolates the starting pitcher matchup and removes bullpen variance.
Favourite. The team expected to win, indicated by a minus sign in American odds (-150) or decimal odds below 2.00.
Grand slam. A home run hit with all three bases occupied, scoring four runs. Rare but game-altering, relevant to live-betting and totals.
Handle. The total amount wagered on a market or event. The global gambling market exceeds 643 billion dollars in annual revenue, and MLB represents roughly 15% of US sports betting handle.
Implied probability. The win probability embedded in a set of odds. Calculated from decimal odds as 1 / decimal odds. Used to compare the bookmaker’s assessment against your own analysis.
Juice (or vig). The bookmaker’s margin built into the odds. On a dime-line MLB market, the juice is approximately 2% — lower than virtually any other major sport.
K/9. Strikeouts per nine innings pitched. A key metric for evaluating starting pitchers and pricing strikeout props.
Listed pitcher. A bet type where the wager is void if the specified starting pitcher does not start the game. The safer option for bettors whose analysis is pitcher-driven.
Terms M to Z
Moneyline. A bet on which team will win the game, with no spread or handicap. The primary MLB market and the one with the thinnest bookmaker margin.
No action. A voided bet, typically triggered when a listed pitcher is scratched or a game is postponed. Your stake is returned in full.
Over/under (O/U). A bet on whether the total runs scored by both teams will be above or below a set number. Also called the totals market.
Parlay (accumulator). A single bet combining multiple selections, all of which must win for the bet to pay. Margin compounds with each leg, making parlays structurally less favourable than straight bets.
Prop bet (proposition bet). A wager on a specific in-game event or player performance rather than the overall game outcome — for example, a pitcher’s strikeout total or a batter’s hit count.
Run line. MLB’s version of the spread, fixed at -1.5 for the favourite and +1.5 for the underdog. The favourite must win by two or more runs to cover the run line.
Same-game parlay (SGP). A parlay where all legs come from a single game, with the bookmaker pricing the correlation between outcomes. Margins are significantly higher than on standard parlays.
Scratched. When a starting pitcher is removed from the scheduled lineup before the game begins, typically due to injury or illness. Triggers a void on listed pitcher bets.
Total (game total). The bookmaker’s projection of combined runs scored by both teams. Standard MLB totals range from 7.0 to 10.0 depending on the pitching matchup and venue.
Underdog. The team expected to lose, indicated by a plus sign in American odds (+130) or decimal odds above 2.00.
Value bet. A bet where the implied probability is lower than the bettor’s assessed probability of the outcome — the fundamental concept behind profitable long-term wagering.
Walk-off. A game-ending play in the bottom of the final inning where the home team scores the winning run. Relevant to live-betting momentum and moneyline settlement.
wOBA (weighted on-base average). An advanced batter metric that assigns run values to each type of offensive outcome. More predictive of future performance than traditional batting average. If any of these terms felt unfamiliar, our step-by-step walkthrough for UK beginners puts them in context with a practical guide to placing your first baseball wager.
xERA (expected ERA). A pitcher metric that models earned run average based on the quality of contact allowed, strikeout rate, and walk rate. Useful for identifying pitchers whose traditional ERA misrepresents their true quality.
What does juice mean in baseball betting?
Juice — also called vig or vigorish — is the margin the bookmaker charges on a bet. In MLB, the standard juice on a dime-line moneyline is approximately 2%, which is lower than the margin on most other major sports. The juice is embedded in the odds rather than charged separately, which means you pay it automatically every time you place a bet. Lower juice means more of your stake goes toward potential profit rather than toward the bookmaker’s revenue.
Is there a difference between action and listed pitcher for UK sportsbooks?
Yes. An action bet remains live regardless of pitching changes before the game, with the odds adjusted automatically if a starter is scratched. A listed pitcher bet is voided if either starting pitcher changes, and your stake is returned. Not all UK sportsbooks offer both options — some default to one rule without giving you a choice. Check your sportsbook’s MLB terms to confirm which rule applies to your bets.
Created by the ”Online Baseball Betting” editorial team.
