MLB analytics blog

• How to Read Pitcher Stats: ERA, WHIP, K/9, BB/9 and K% — What ERA, WHIP, K/9, BB/9, K%, BB% and HR/9 measure, how each is calculated, a worked example from one stat line, and which numbers matter most.
• What Is FIP? FIP, xFIP and xERA Explained With Examples — FIP rebuilds ERA from strikeouts, walks, hit batters and home runs; xFIP normalises home runs; xERA uses Statcast contact quality. Formulas, a worked example and when to use each.
• How the BullpenEdge MLB Projection Model Works — Starters, bullpens, lineups, ballparks and weather go in; a calibrated win probability, projected score and run distribution come out. Here is every step.
• What a Win Probability Actually Means (and How to Judge One) — A 60% projection that loses is not wrong. How to read a baseball win probability, why calibration matters more than picking winners, and how we measure it.
• How We Grade Our Own Projections — Projections are locked before first pitch and graded automatically. Here is exactly what is recorded, what is measured, and why nothing can be edited after the fact.
• Projecting Pitchers with the Marcel Method — Why a starter's last three starts say so little, how much history each stat needs, and how BullpenEdge blends seasons and regresses to the league average.
• Bullpen Fatigue and Availability: What the Data Says — How BullpenEdge decides which relievers are available, what three days of pitch counts reveal, and how much a tired bullpen really changes a game.
• Starters vs Bullpens: How Innings Are Split in Today's MLB — Starters now get about 15 outs a night. What that means for projecting a game, why a starter's expected innings matter as much as his quality, and how openers are handled.
• MLB Park Factors Ranked: Which Ballparks Add Runs in 2026 — Coors Field adds more than 20% to scoring; T-Mobile Park takes almost 10% away. All 30 parks ranked with multi-year, regressed run factors.
• How Weather Affects MLB Scoring: Temperature and Wind in Numbers — Games above 85°F average 9.8 runs; games below 55°F average 8.2. What 2021–2026 data says about temperature, wind direction and roofs.
• Home-Plate Umpires and Run Scoring: Real Effect or Noise? — Some umpires really do run bigger or smaller strike zones, but the effect is smaller than most think: about a tenth of a run per game for a typical umpire.
• Platoon Splits Explained: Why Handedness Matters — Hitters do better against opposite-handed pitchers. How BullpenEdge measures the platoon advantage of a lineup, and why individual hitters' splits are mostly noise.
• Run Distributions in Baseball: Why Poisson Isn't Quite Enough — Teams are shut out 6.5% of the time and score ten or more 7.5% of the time. Why baseball scoring is more spread out than a Poisson curve, and the odd-number quirk in game totals.
• What Drives MLB Run Totals: The Factors Ranked — Which inputs move a game's projected runs the most? Strikeout pitching, the ballpark and temperature lead; umpires and bullpen rest trail. Ranked from the fitted model.
• MLB Win Margins: One-Run Games and Comfortable Wins — About 28% of MLB games are decided by one run. How often favourites win by two or more, and how the model estimates margins from full run distributions.
• MLB Home-Field Advantage: How Big Is It Really? — Home teams won 52.1% to 55.0% of games each season since 2019. Why the advantage is smaller in baseball than in other sports and how the model handles it.
• Early-Season Stats and Small Samples: What to Trust in April — A hitter's April wOBA correlated only 0.13–0.18 with the rest of his season; last season's wOBA correlated 0.47–0.54. The numbers behind regression to the mean.
• Common Mistakes When Reading Baseball Stats — ERA with a bad defense behind it, batting average on 40 at-bats, head-to-head records from five years ago. Seven habits that make baseball numbers mislead, and what to use instead.
• MLB Playoff Format Explained: How Many Games in Each Round — How the 12-team MLB postseason works: byes, seeding, and how many games the Wild Card Series, ALDS, NLDS, ALCS, NLCS and World Series can last.
• How to Read a Pitcher Projection: K%, BB%, HR% and Expected Innings — What each number on a BullpenEdge pitcher projection means: strikeout, walk and home-run rates, expected innings, regression to league average, Statcast context and recent starts.

BullpenEdge publishes MLB statistics and model projections for analysis and entertainment. Projections are estimates, can be wrong, and are not advice of any kind. Not affiliated with Major League Baseball. See the Disclaimer and Methodology.