MLB Betting Glossary — EV, Vig, NRFI, Barrel Rate & More | Mongoose Bets
MLB Betting & Analytics Glossary
Plain-language definitions of the betting and baseball terms used across Mongoose Bets — from expected value and vig-free fair odds to NRFI, barrel rate, and the Mongoose Score. Every projection on the site is derived from 2,500 Monte Carlo simulations per game; these are the concepts behind the numbers.
Expected Value (EV)
What is expected value in sports betting?
- Expected value (EV) is the average profit or loss a bet would return if you placed it many times. A positive-EV (+EV) bet is one where your estimated probability of winning, multiplied by the payout, exceeds the stake. Over a large sample, +EV bets are profitable regardless of short-term variance. Mongoose Bets flags a bet as +EV when its simulated probability is higher than the vig-free probability the sportsbook is implying.
Edge
What is edge in sports betting?
- Edge is the gap between the true probability of an outcome and the probability the sportsbook implies with its odds after the vig is removed. A +5% edge means the model believes the outcome is five percentage points more likely than the book is pricing. Edge is the core number Mongoose Bets ranks every play by.
Vig (Juice)
What is the vig in sports betting?
- The vig (short for vigorish), also called juice, is the sportsbook's built-in margin — the reason a two-sided market's implied probabilities add up to more than 100%. A standard -110/-110 market carries about 4-5% vig; player props often carry 6-8%, and alt lines can exceed 10%. Removing the vig reveals the market's true implied probability.
No-Vig Fair Odds
What are no-vig (vig-free) fair odds?
- No-vig fair odds strip the sportsbook's margin out of a market to show the true implied probability of each outcome. You convert each side to implied probability, sum them (the total exceeds 100% by the vig), then divide each side by that sum. Mongoose Bets compares its simulated probability against vig-free fair odds, not the raw posted line.
Implied Probability
What is implied probability?
- Implied probability is the win probability that a set of betting odds represents. American odds of -150 imply about 60%, and +150 imply about 40%. Because the vig inflates both sides, raw implied probabilities sum to more than 100%; devigging normalizes them back to a fair 100%.
Monte Carlo Simulation
What is a Monte Carlo simulation in sports betting?
- A Monte Carlo simulation estimates the probability of an outcome by playing it out thousands of times with realistic randomness. Mongoose Bets simulates every MLB game 2,500 times using real lineups, pitcher matchups, ballpark factors, weather, and umpire tendencies, then aggregates the results into win probabilities, predicted scores, and player-prop projections.
NRFI / YRFI
What is NRFI in baseball betting?
- NRFI stands for No Runs First Inning — a bet that neither team scores in the opening frame. The opposite is YRFI (Yes Runs First Inning). Mongoose Bets derives NRFI probabilities by simulating the first inning 2,500 times per game, accounting for both starting pitchers’ first-inning splits, the leadoff hitters, and park context.
Moneyline
What is a moneyline bet?
- A moneyline bet is a wager on which team wins the game outright, with no point spread. Odds are quoted in American format: a negative number is the favorite (the amount you stake to win $100) and a positive number is the underdog (the amount you win on a $100 stake). Mongoose Bets prices every moneyline against its 2,500-sim win probability.
Run Total (Over/Under)
What is a run total (over/under) in baseball?
- A run total is a bet on the combined runs both teams score, set as an over/under line by the sportsbook. Mongoose Bets simulates each game 2,500 times to build a distribution of total runs, then compares the model’s over and under probabilities to the book’s price to find totals value — factoring in starting pitchers, bullpens, park, weather, and the plate umpire.
Total Bases
What are total bases in a player prop?
- Total bases counts the bases a hitter earns from hits: one for a single, two for a double, three for a triple, and four for a home run. A common prop is 2+ total bases. Mongoose Bets projects each hitter’s total-base distribution from the simulation and prices it against the sportsbook line.
Barrel Rate
What is barrel rate in baseball?
- Barrel rate is the share of a hitter’s batted balls that are "barrels" — the ideal combination of exit velocity and launch angle (roughly 98+ mph at 26-30 degrees) that produces extra-base hits and home runs at the highest rates. It is a Statcast metric and a strong leading indicator of power, so Mongoose Bets weighs it in home-run projections.
ISO (Isolated Power)
What is ISO (isolated power) in baseball?
- ISO, or isolated power, measures a hitter’s raw power by counting only extra bases: slugging percentage minus batting average. A single adds nothing to ISO; a home run adds three. League-average ISO sits around .160, and .250+ marks elite power. It isolates power from the ability to simply make contact.
Park Factor
How do park factors affect MLB betting?
- A park factor adjusts how often events — hits, home runs, runs — occur at a given ballpark relative to league average. Coors Field inflates run scoring roughly 12% above neutral, while Oracle Park suppresses home runs by about 15%. Mongoose Bets applies per-event park multipliers on every simulated plate appearance.
Statcast
What is Statcast?
- Statcast is MLB’s tracking system that measures the physics of every pitch and batted ball — exit velocity, launch angle, sprint speed, spin rate, and more. Mongoose Bets uses Statcast batted-ball data as a core input to its simulation because it describes underlying skill better than surface stats that are noisy over small samples.
Kelly Criterion
What is the Kelly criterion?
- The Kelly criterion is a formula for the optimal fraction of your bankroll to stake on a bet, based on your estimated win probability and the offered odds. It maximizes long-run growth but assumes your probability estimate is exact, so most bettors use fractional Kelly (a quarter or half of full Kelly) to cut variance and protect against estimation error.
Arbitrage Betting
What is arbitrage betting?
- Arbitrage betting means backing every outcome of a market across different sportsbooks so you lock in a guaranteed profit no matter who wins. It works when the best available prices imply a total probability below 100%. Returns are typically small (0.5-3%), and books may limit accounts that arb consistently.
Closing Line Value (CLV)
What is closing line value (CLV)?
- Closing line value is the difference between the odds you bet and the final ("closing") odds just before the event starts. Consistently beating the closing line is the strongest evidence a bettor is +EV, because the closing line is the market’s most accurate price. Mongoose Bets grades its record at closing odds for this reason.
Brier Score
What is a Brier score?
- A Brier score measures how well-calibrated probability predictions are: the average squared difference between the predicted probability and the actual 0/1 outcome. Lower is better, and 0 is perfect. Mongoose Bets tracks Brier scores to verify that when the model says 25%, the outcome really happens about 25% of the time.
Mongoose Score
What is the Mongoose Score?
- The Mongoose Score is a 0-100 rating that condenses a play’s full picture into one number — blending the model’s simulated probability, the edge versus the market price, and supporting context like recent form and matchup. On the HR Zone board it is the Zone Score for home-run potential. Higher means the model is more confident the bet has value.
Want to see these concepts applied to tonight's slate? Read the full methodology or explore the day's best bets.