Research
MLB roof open vs closed: does it change scoring?
Seven MLB parks can open or close their roof on game day. Forecast sites treat an open roof as a weather game and a closed roof as neutral. We checked whether the roof decision actually moves runs, home runs or results against the betting total.
The headline
Across 3,281 games at 7 retractable-roof parks from 2021 to 2026, opening the roof made no measurable difference to scoring once each game is compared with its own park and season — and the closing total already priced it.
Runs, open vs closed
+0.13
t = 0.87
Home runs, open vs closed
+0.07
t = 1.26
Vs closing total, open vs closed
-0.10
t = -0.66
None of the three gaps clears our |t| ≥ 1.96 bar. This is a null result, published as one.
Open vs closed, all parks
| Roof | Games | Avg temp °F | Runs | Home runs | Runs vs close | Over rate |
|---|---|---|---|---|---|---|
| Open | 1,159 | 73.6 | 8.56 | 2.36 | +0.41 | 50.0% |
| Closed | 2,122 | 81.5 | 8.71 | 2.23 | +0.51 | 50.1% |
Raw averages. Both roof states finished slightly above the closing total, in line with the small league-wide Over drift in this period — the gap between them is what matters.
Park by park
| Park | Open / closed games | Runs open / closed | HR open / closed | Temp open / closed | Vs close open / closed |
|---|---|---|---|---|---|
| American Family Field | 258 / 218 | 8.60 / 8.51 | 2.38 / 2.25 | 75.8 / 58.6 | +0.44 / +0.57 |
| Chase Field | 118 / 356 | 9.74 / 9.44 | 2.14 / 2.05 | 88.0 / 99.1 | +0.73 / +0.68 |
| Globe Life Field | 59 / 415 | 9.36 / 8.53 | 2.51 / 2.39 | 76.8 / 86.9 | +0.77 / +0.26 |
| Marlins Park | 42 / 432 | 8.69 / 8.58 | 1.79 / 1.99 | 78.8 / 83.7 | +0.48 / +0.75 |
| Minute Maid ParkToo few games to read | 11 / 466 | 9.27 / 8.71 | 2.73 / 2.46 | 76.6 / 84.2 | +0.50 / +0.45 |
| Rogers Centre | 269 / 163 | 8.86 / 8.66 | 2.48 / 2.25 | 72.9 / 58.1 | +0.44 / +0.38 |
| T-Mobile Park | 402 / 72 | 7.83 / 7.75 | 2.35 / 2.18 | 67.3 / 53.9 | +0.21 / +0.29 |
Per-park splits are descriptive only and were not tested individually. Globe Life Field's open-roof games scoring more is a small sample (59 games) and should be read as directional.
Method
- Games at retractable-roof parks, 2021–2026, with roof state recorded from the official game feed.
- Each game's runs and home runs are measured against its own park-season average; open and closed are then compared with a Welch t-test.
- Closing totals are the last consensus line from ESPN (single source); 3,278 games have one.
- We only call a gap real at |t| ≥ 1.96 and require 40 games per group. Nothing here was chosen after looking at the data.
Related research
Where this is applied
These findings feed the game-time read on every MLB venue page, using the same sample-size and significance rules published here.
OverUnderWeather Research Desk
Independent data analysis on public sports and weather records. Studies match historical game outcomes to archived game-window weather, apply pre-set sample and significance rules, and publish null results when that is what the data show. Editorial policy and corrections log.
Frequently asked
Do MLB games score more with the roof open?
Barely, and not by a margin we can separate from noise. Measured against the same park in the same season, roof-open games scored about 0.13 more runs (t = 0.87) and 0.07 more home runs (t = 1.26) than roof-closed games across seven retractable-roof parks since 2021.
Should I adjust a total when a retractable roof opens?
Our data says the market already handles it. Against the closing total, open-roof games finished 0.10 runs lower relative to the line than closed-roof games (t = −0.66), and both went Over almost exactly half the time. There is no roof edge to chase.
Why is the raw open vs closed comparison misleading?
Roofs close for heat, cold and rain, so closed games are not a random sample. Raw averages mix in park and season differences. Every headline figure here compares each game with its own park and season, which removes most of that mix.
Which parks are included?
American Family Field, Chase Field, Globe Life Field, loanDepot park (Marlins Park), Minute Maid Park, Rogers Centre and T-Mobile Park. Fully enclosed domes are excluded. Parks with fewer than 40 games in one roof state are shown but flagged as too thin to read.