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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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Aaron O'Donell | 2032-2033 | 4 | 0 | 1.000 | 4.85 | 33 | 0 | 0 | 0 | 0 | 26.0 | 29 | 14 | 4 | 15 | 26 |
| Leon O'Donnell | 2025-2033 | 23 | 25 | .479 | 5.49 | 80 | 72 | 1 | 0 | 1 | 416.1 | 533 | 254 | 60 | 120 | 248 |
| Ken O'Slattery | 2030-2033 | 9 | 9 | .500 | 4.05 | 171 | 0 | 0 | 0 | 3 | 197.2 | 170 | 89 | 27 | 117 | 179 |
| Mitsuhide Oda | 2020-2023 | 0 | 0 | .000 | 8.68 | 7 | 0 | 0 | 0 | 0 | 9.1 | 12 | 9 | 0 | 11 | 5 |
| Lanny Odegaard | 2010-2025 | 36 | 46 | .439 | 5.01 | 354 | 76 | 0 | 0 | 25 | 703.0 | 771 | 391 | 82 | 348 | 408 |
| Kinnosuke Ogawa | 2016-2016 | 7 | 1 | .875 | 3.47 | 61 | 0 | 0 | 0 | 3 | 85.2 | 75 | 33 | 10 | 18 | 67 |
| Mitsuzuka Ogawa | 2017-2028 | 65 | 98 | .399 | 4.63 | 494 | 219 | 1 | 0 | 35 | 1501.2 | 1566 | 773 | 160 | 673 | 888 |
| Tomokazu Ohka | 1999-2009 | 44 | 60 | .423 | 4.21 | 235 | 145 | 3 | 0 | 4 | 962.0 | 1056 | 450 | 52 | 282 | 551 |
| Will Ohman | 2003-2008 | 6 | 6 | .500 | 4.24 | 155 | 0 | 0 | 0 | 8 | 150.2 | 145 | 71 | 9 | 69 | 100 |
| Tsugumichi Ojima | 2024-2031 | 16 | 9 | .640 | 6.35 | 212 | 22 | 1 | 0 | 4 | 307.2 | 296 | 217 | 56 | 302 | 259 |
| Felipe Olberos | 2031-2032 | 0 | 0 | .000 | 6.75 | 6 | 0 | 0 | 0 | 0 | 5.1 | 5 | 4 | 0 | 3 | 6 |
| Logan Oldham | 2009-2019 | 101 | 82 | .552 | 3.86 | 518 | 169 | 9 | 2 | 6 | 1491.1 | 1558 | 640 | 134 | 493 | 814 |
| Darren Oliver | 1993-2002 | 71 | 65 | .522 | 5.02 | 246 | 186 | 10 | 4 | 2 | 1154.0 | 1303 | 644 | 0 | 500 | 700 |
| Stanton Oliver | 2028-2032 | 7 | 17 | .292 | 6.46 | 72 | 34 | 0 | 0 | 1 | 210.1 | 269 | 151 | 36 | 122 | 145 |
| Kevin Olsen | 2001-2013 | 64 | 55 | .538 | 4.70 | 565 | 118 | 3 | 1 | 9 | 1201.0 | 1311 | 627 | 91 | 413 | 828 |
| José Ontiveros | 2028-2033 | 48 | 28 | .632 | 4.80 | 217 | 94 | 2 | 2 | 1 | 646.1 | 716 | 345 | 73 | 338 | 442 |
| Alfredo Ordóńez | 2031-2033 | 11 | 14 | .440 | 5.03 | 133 | 7 | 0 | 0 | 1 | 196.2 | 203 | 110 | 24 | 95 | 130 |
| Ismael Orgega | 2025-2027 | 4 | 6 | .400 | 9.63 | 38 | 9 | 0 | 0 | 0 | 75.2 | 104 | 81 | 12 | 73 | 51 |
| Jesse Orosco | 1979-2002 | 85 | 78 | .521 | 3.04 | 1187 | 4 | 0 | 0 | 142 | 1261.1 | 1014 | 426 | 0 | 560 | 1150 |
| António Ortega | 2028-2033 | 18 | 16 | .529 | 3.92 | 227 | 1 | 0 | 0 | 71 | 213.1 | 206 | 93 | 20 | 102 | 148 |
| Jorge Ortega | 2028-2029 | 1 | 0 | 1.000 | 6.48 | 8 | 0 | 0 | 0 | 0 | 8.1 | 10 | 6 | 1 | 13 | 8 |
| José Ortíz | 2023-2025 | 1 | 2 | .333 | 10.58 | 26 | 0 | 0 | 0 | 0 | 32.1 | 36 | 38 | 5 | 36 | 24 |
| Júlio Ortíz | 2021-2031 | 36 | 46 | .439 | 5.72 | 553 | 0 | 0 | 0 | 60 | 584.0 | 655 | 371 | 90 | 326 | 435 |
| Mario Ortíz | 2030-2033 | 12 | 12 | .500 | 4.21 | 139 | 11 | 0 | 0 | 4 | 216.0 | 212 | 101 | 20 | 114 | 193 |
| Pepe Ortíz | 2014-2025 | 28 | 30 | .483 | 6.15 | 265 | 47 | 1 | 0 | 4 | 544.1 | 670 | 372 | 103 | 223 | 178 |
| Russ Ortiz | 1998-2008 | 121 | 92 | .568 | 4.39 | 383 | 279 | 10 | 3 | 3 | 1834.1 | 1718 | 895 | 58 | 1017 | 1219 |
| Leonard Oshields | 2011-2014 | 5 | 2 | .714 | 5.63 | 59 | 1 | 0 | 0 | 0 | 46.1 | 57 | 29 | 3 | 26 | 37 |
| Roy Oswalt | 2001-2012 | 109 | 70 | .609 | 4.04 | 608 | 162 | 7 | 3 | 11 | 1575.1 | 1550 | 708 | 131 | 575 | 1528 |
| Yic Ow-Yang | 2020-2033 | 59 | 77 | .434 | 6.29 | 696 | 73 | 1 | 0 | 22 | 1019.0 | 1270 | 712 | 170 | 413 | 655 |
| Willie Owens | 2021-2021 | 0 | 0 | .000 | 27.00 | 1 | 0 | 0 | 0 | 0 | 0.1 | 1 | 1 | 0 | 3 | 0 |
| Player | From-To | W | L | Pct | ERA | G | GS | CG | SHO | SV | IP | H | ER | HR | BB | SO |
| Atsumori Ozawa | 2015-2015 | 0 | 0 | .000 | 4.50 | 2 | 0 | 0 | 0 | 0 | 2.0 | 2 | 1 | 1 | 1 | 1 |
