Using Advanced Stats in Over/Under Baseball Bets

Stats, MLB Logo, Bryce Harper
The history of baseball is intrinsically intertwined with gambling.

The Blacksox Scandal of 1919 involved 8 Chicago White Sox players being accused of throwing the 1919 World Series to the Cincinnati Reds. The team was accused of taking money from a gambling syndicate led by Arnold Rothstein and 8 players from that team were banned from baseball for life.

This criminal act changed the game of baseball forever and resulted in Kenesaw Mountain Landis being appointed as the first commissioner— his duty was to restore the public’s faith in baseball.

Even though a betting scandal changed the game of baseball forever, baseball betting is still alive and well as sportsbooks around the country offer baseball betting year-round.

What Are Baseball Over/Under Bets?

An over/under bet in baseball is simple enough to make. The oddsmakers will give you an over/under like 6.5, which is the number of runs both teams will score added together. Then you’ll either bet “over” that number or “under” that number.

An over bet means you think the total runs between the two teams will be over 6.5.
An under bet means you think the total runs between the two teams will be under 6.5.

If you pick the over, you’re probably expecting both teams to have big offensive nights. This can be because both pitching staffs are fatigued or not very good, or because both teams just have some tremendous power hitters.

You may choose to make an under bet when one of the team’s starting pitchers is an ace. An ace pitcher, like Max Scherzer, is one of the top 30 or so pitchers in the league. Aces are expected to give up around 3 runs or less on an average night and cause the run total to lean towards the under.

Over/unders are different from other bets though in one key area. Over/under bets are not valid unless the game goes the whole 9 innings.

How to Understand Odds in Baseball Over/Under Bets

When you make an over/under bet, you’re not betting on which team will win—so it doesn’t matter which team you think is superior or is your favorite. You’re betting on how well the offenses— or conversely how bad the pitchers will do— on that night.

The over/under odds will look something like this for a Yankees Red Sox game:

  • Line: 6.5
  • Over (-110)
  • Under (+120)

If you want to bet on the over, you’ll need to bet $110 to win $100.

If you want to bet on the under, you’ll need to bet $100 to win $120.

As you can see, you can make more money per dollar by betting on the under than the over in this scenario. The oddsmakers set the odds in favor of certain sides to draw bettors into those sides and make money off the losing bets.

How to Predict Runs Scored

Now that you understand what an over/under bet is, how odds work, and how the payouts work, you can start thinking about making some over/under bets.

Runs scored is the determining factor of an over/under bet, so you need to look at how well the overall offense works.

OPS is the sum of a player’s slugging average and on-base percentage.

Team OPS indicates the average OPS for the whole team and is a better indicator of total runs scored than one player’s batting average.

The strength of a team’s offense is an important factor, but pitching and fielding of the opposing team can suppress even the most potent of offenses.

While many bettors use traditional stats like ERA(earned-run average) and RBI’s(runs batted-in) to place their over/under bets, these stats are not as predictive as advanced stats like ERA+ and OPS+. (Available at Baseball-Reference)

You can be more accurate when making over/under bets by using these advanced statistics that do a much better job of predicting runs scored than traditional stats.


Before we can show you how effective ERA+ is at predicting runs scored, we’ll discuss why using ERA stats are less useful when making wagers.

Despite it’s less predictive nature, earned run average (ERA) is historically one of the most popular baseball stats. Henry Chadwick came up with the stat in the early 1900s when relief pitchers became necessary.

Before then, almost every starting pitcher would pitch a complete game so relief pitchers were not commonly used.

Once relief pitchers started pitching more often, it became necessary to calculate ERA to determine which pitchers gave up the least amount of runs.

Aroldis Chapman

Many traditional gamblers still use ERA to predict which pitcher will be more effective when making over/under bets.

In this example of using ERA to predict an over/under bet, the game’s over/under will be set at 7.

If both starting pitchers have an ERA of 2.3, then you could expect the total runs scored in the game to be slightly higher than 4.6. Each starting pitcher will give up between 2 to 3 runs and the bullpen may give up another run or two for each team.

Since both teams have starting pitchers with low ERAs, most traditional bettors would take the under.

While this is a sound strategy, the oddsmakers will know this and favor the under in a game with two great starting pitchers. This is where ERA+ can be useful.

ERA+ is a weighted average of ERA that uses ballpark factors and league average ERAs in its calculation. This makes ERA+ better for comparing pitchers who pitch in different ballparks and gives bettors a more true indication of which pitchers are actually better at preventing runs.

ERA+ will either be a number less or greater than 100. The further away the number is from 100, the further away the pitcher is from league average.

Pedro Martinez has the modern record for ERA+ in one season at 291, indicating he was 191% better than league average that season.

Pedro Martinez

While ERA is a good, general indicator of how good a pitcher is, it doesn’t account for what the average ERA of the league is, or if the pitcher pitches in a pitcher-friendly ballpark. ERA+ does a better job of showing how pitchers compare to the rest of the league.

You can use ERA+ to gain an advantage in over/under bets. If a starting pitcher has an ERA+ of 120, he’s 20% better than the league average so you may want to take the under on the bet.

ERA+ helps bettors see which pitchers are really effective and which ones just play in a beneficial park.


While ERA+ is used to determine how effective pitchers are compared to league average, On-base Plus Slugging Plus (OPS+) is used to determine how effective hitters are against the entire league and can give you an advantage when making over/under bets.

Many bettors would incorrectly use batting average to see how many runs a team will score when they’re making an over/under bet. While batting average is good for showing how many hits a player gets and how good his contact skill is, it doesn’t show you how good of an offensive player he is.

OPS considers how many walks and extra-base hits a player gets while batting average is calculated solely off hits. Walks and extra-base hits both contribute to runs scored as much as hits do, so leaving them out makes batting average an inferior stat.

Walk in Baseball

OPS+ takes the greatness of OPS one step further and compares the OPS of players to the league average OPS. OPS+ works in the same way that ERA+ does— the number is scaled to 100. The further a player’s OPS+ is from 100, the further that player is from league average, positive or negative.

So a player with a 150 OPS+ is 50% better than league average while a player with an OPS+ of 75 is 25% worse than league average.

OPS+ can show you how much better a team’s offense is than a league-average offensive team. This is much more useful than OPS when predicting whether to bet over or under on a team because it does not consider the conditions of each ballpark.

Both OPS+ and ERA+ can more truthfully show you how good players are while ignoring park effects. The stats are more effective than traditional stats like ERA or batting average at predicting how many runs a team will score.

You can even compare a team’s OPS+ to their opponent’s ERA+ to see which team is further from league average offense or pitching, which will give you a big leg up on bettors who only look at stats like ERA and batting average.


What’s your favorite advanced baseball statistic to use when betting on over/unders? Let us know in the comments.