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| League History Index | Players | Teams | Managers | Leagues | Leaderboards | Awards | Accomplishments |
| Player | From-To | W | L | Pct | ERA | G | GS | CG | SHO | SV | IP | H | ER | HR | BB | SO |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Brian O'Brian | 2013-2022 | 1 | 0 | 1.000 | 15.00 | 1 | 0 | 0 | 0 | 0 | 3.0 | 7 | 5 | 0 | 1 | 0 |
| Paul O'Callahan | 2020-2022 | 0 | 0 | .000 | 7.31 | 16 | 0 | 0 | 0 | 1 | 28.1 | 36 | 23 | 5 | 17 | 13 |
| Anderson O'Mara | 2026-2033 | 17 | 16 | .515 | 3.43 | 187 | 0 | 0 | 0 | 34 | 251.2 | 236 | 96 | 32 | 54 | 158 |
| Ron O'Slattery | 2020-2021 | 1 | 1 | .500 | 9.58 | 4 | 1 | 0 | 0 | 0 | 10.1 | 20 | 11 | 0 | 1 | 4 |
| Jake O'Tomalty | 2019-2027 | 2 | 2 | .500 | 3.02 | 33 | 0 | 0 | 0 | 2 | 41.2 | 39 | 14 | 5 | 17 | 28 |
| Alin Oanta | 2021-2022 | 8 | 9 | .471 | 4.95 | 35 | 16 | 0 | 0 | 1 | 100.0 | 97 | 55 | 14 | 51 | 68 |
| Goodluck Obasanjo | 2032-2034 | 6 | 3 | .667 | 3.92 | 37 | 0 | 0 | 0 | 5 | 57.1 | 50 | 25 | 5 | 39 | 41 |
| Piotr Oja | 2030-2034 | 24 | 23 | .511 | 3.89 | 135 | 37 | 1 | 1 | 7 | 404.2 | 388 | 175 | 45 | 141 | 385 |
| Jesús Olvero | 2021-2023 | 2 | 7 | .222 | 4.23 | 58 | 0 | 0 | 0 | 12 | 78.2 | 71 | 37 | 7 | 49 | 59 |
| Juan Ordóńez | 2032-2032 | 0 | 2 | .000 | 6.07 | 3 | 3 | 0 | 0 | 0 | 13.1 | 20 | 9 | 2 | 1 | 2 |
| Ramón Ortega | 2013-2028 | 131 | 75 | .636 | 3.21 | 314 | 261 | 39 | 12 | 5 | 1935.1 | 1624 | 690 | 189 | 547 | 1849 |
| Roberto Ortega | 2019-2020 | 8 | 10 | .444 | 3.26 | 27 | 27 | 3 | 0 | 0 | 190.2 | 190 | 69 | 11 | 31 | 132 |
| José Ortíz | 2023-2028 | 2 | 5 | .286 | 3.44 | 31 | 0 | 0 | 0 | 5 | 34.0 | 51 | 13 | 4 | 13 | 28 |
| Pedro Ortíz | 2020-2034 | 32 | 26 | .552 | 3.50 | 133 | 63 | 3 | 0 | 3 | 485.2 | 453 | 189 | 31 | 182 | 380 |
| Vincente Ortíz | 2023-2028 | 0 | 4 | .000 | 7.88 | 35 | 0 | 0 | 0 | 0 | 53.2 | 68 | 47 | 4 | 45 | 19 |
| Richard Osborn | 2029-2034 | 3 | 3 | .500 | 4.35 | 38 | 0 | 0 | 0 | 1 | 62.0 | 69 | 30 | 9 | 17 | 57 |
| Jorge Otero | 2031-2034 | 29 | 15 | .659 | 3.18 | 78 | 78 | 0 | 0 | 0 | 453.0 | 412 | 160 | 45 | 115 | 421 |
| Yajirobei Otomo | 2028-2034 | 11 | 8 | .579 | 2.93 | 64 | 0 | 0 | 0 | 4 | 138.1 | 99 | 45 | 11 | 37 | 122 |
| Bill Oulton | 2021-2034 | 93 | 56 | .624 | 3.13 | 210 | 199 | 7 | 1 | 0 | 1375.2 | 1209 | 478 | 93 | 533 | 1065 |
| Mike Owens | 2029-2032 | 0 | 6 | .000 | 8.16 | 10 | 8 | 0 | 0 | 0 | 43.0 | 50 | 39 | 5 | 26 | 27 |
