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When betting on MLB, sharp edges often lie beyond starting pitchers and batting averages.
One of the most overlooked yet high-impact variables is bullpen health and effectiveness. Understanding how a team’s relievers have been used, and how well they perform can provide critical insight for betting full-game totals, moneylines, live bets, and late-inning performance.
This guide breaks down how to use key bullpen metrics to gain an edge.
In Outlier, you will find the bullpen and relief pitcher data in the Matchup tab for any MLB Game or Player Prop market.
Bullpen Metrics Breakdown and How to Use Them
Stat | What It Tells You | How to Use It for Betting |
PC L3 / PC L5 (Pitch Count, Last 3/5 Days) | Recent workload. High pitch counts = possible fatigue or unavailability. | Fade teams with overworked bullpens, especially if the starter is likely to have a short outing. Look for over bets on total runs or live bet overs after starter exits. |
Rest | Days off since last appearance. 0 = pitched yesterday. | A bullpen with multiple pitchers on 0–1 days rest is more likely to perform poorly. |
ERA | Run prevention, but noisy in small samples. | Use directionally. A high ERA paired with high usage = potential liability. Focus more on K% and usage. |
K% | Strikeout rate, a cleaner skill indicator than ERA. | High K% = better ability to escape jams. Low K%, high usage = dangerous combo. Use to spot bullpen mismatches. |
Practical Examples for Using Bullpen Data
1. Totals Bets (Full Game Over/Under)
If both bullpens are rested and feature high K% arms, lean under.
If one or both are overworked and have low K%, lean over, especially if starters are mid-tier.
2. First 5 Innings vs Full Game
If the starter is strong but bullpen is gassed, consider:
First 5 under / ML but fade full game bets.
Live bet against the team after 6th inning.
3. Team Totals / Late Inning Live Bets
Opposing team has tired arms and no rest? Look to:
Live bet overs after starter exits.
Target player props (e.g., RBI or hits) for teams facing tired bullpens.
4. Same-Game Parlays
Combine overworked bullpen + low K% with opponent hitters' props.
Example: If E. Pagán has thrown 37 pitches in 3 days and is the Reds’ top reliever, parlay a game total over with an opposing team total or hit props.
MLB Betting Strategy Tip
Track usage patterns:
If multiple relievers have >30 pitches in the last 3 days and 0 rest, they’re either unavailable or ineffective. Teams might turn to lower-leverage arms or long relievers.
Example from image above:
G. Ashcraft (52 pitches L3, 0 rest) — very likely unavailable or fatigued.
S. Moll (9.00 ERA, 22.2% K%) with high usage — red flag if he's forced in.
If this is the state of the bullpen and the Reds are in a close game, bet on ATL live or take ATL team total over late.
Bullpen data is a hidden gem for MLB bettors who want to go deeper than surface-level stats. By tracking recent pitch counts, rest days, ERA, and strikeout rates, you can spot tired bullpens, late-game vulnerabilities, or mismatches that the average bettor overlooks.
Whether you're betting totals, team props, or live lines, factoring in bullpen conditions can give you the edge needed to outsmart the market.