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| Single-Season Losses Leaderboard | |
| * - Indicates Hall of Fame |
| Rank | Player | Losses | IP | Year | Career Leaderboard |
| 1. | John Pueblo | 29 | 205.0 | 2028 | |
| 2. | Jonas Cardenas | 26 | 198.0 | 2024 | |
| 3. | Jose Altamirano | 25 | 247.7 | 2016 | |
| 4. | Fred McFinn | 24 | 198.3 | 2023 | |
| Billy Powell | 24 | 266.0 | 2018 | ||
| Robert Seaborn | 24 | 290.7 | 2003 | ||
| 7. | Bill Rosas | 23 | 222.3 | 2029 | |
| Jake Macfadden | 23 | 164.0 | 2029 | ||
| Kyle Porcaro | 23 | 245.7 | 2009 | ||
| 10. | Ronaldo Laguna | 22 | 223.7 | 2023 | |
| Erik Ram | 22 | 215.7 | 2023 | ||
| Franky Saez | 22 | 173.3 | 2023 | ||
| Franky Saez | 22 | 211.7 | 2021 | ||
| Alfredo Chavira | 22 | 178.3 | 2016 | ||
| James Alexander | 22 | 197.0 | 2013 | ||
| Mario Bloodworth | 22 | 182.3 | 2011 | ||
| Ramon Quintana | 22 | 244.0 | 2008 | ||
| Owen Brunton | 22 | 171.7 | 2007 | ||
| 19. | Al West | 21 | 271.7 | 2029 | |
| Pete Branson | 21 | 181.0 | 2028 | ||
| Patrido Pabtojas | 21 | 227.7 | 2026 | ||
| Skip Witchell | 21 | 209.7 | 2026 | ||
| Yoshino Eda | 21 | 187.0 | 2022 | ||
| Bailey Muldoon | 21 | 183.7 | 2022 | ||
| Bill Rowley | 21 | 183.3 | 2019 | ||
| Matthew Bedard | 21 | 248.3 | 2010 | ||
| Bobb Beasley | 21 | 208.0 | 2010 | ||
| Richard Hirsh | 21 | 279.7 | 2008 | ||
| Jeffrey Cargo | 21 | 226.0 | 2008 | ||
| Nathan Cramer | 21 | 209.0 | 2008 | ||
| Richard Hirsh | 21 | 291.0 | 2007 | ||
| Gregory Hart | 21 | 272.3 | 2007 | ||
| Ramon Quintana | 21 | 242.0 | 2007 | ||
| Tracey Northrup | 21 | 221.3 | 2007 | ||
| Thomas Showers * | 21 | 302.3 | 2005 | ||
| John Seely | 21 | 185.0 | 2000 | ||
| 37. | Quinonez Bythell | 20 | 210.3 | 2029 | |
| Cisco Pacheco | 20 | 199.3 | 2029 | ||
| Jeffrey Anderson | 20 | 195.7 | 2028 | ||
| Cliff Summey | 20 | 182.3 | 2028 | ||
| Robert Silvera | 20 | 206.0 | 2027 | ||
| Cliff Summey | 20 | 186.7 | 2027 | ||
| Keith Davy | 20 | 239.7 | 2024 | ||
| Takeo Ikeda | 20 | 179.7 | 2024 | ||
| David Echegaray | 20 | 187.3 | 2022 | ||
| Simeon Davalos | 20 | 197.3 | 2021 | ||
| Mickey Colt | 20 | 191.0 | 2019 | ||
| Jay Escobar | 20 | 242.0 | 2017 | ||
| Pedro Contreras | 20 | 213.3 | 2017 | ||
| Joseph Clark | 20 | 193.3 | 2017 | ||
| Theodore Tonti | 20 | 250.3 | 2016 | ||
| Almonde Garito | 20 | 233.7 | 2016 | ||
| Donn Fagan | 20 | 184.7 | 2016 | ||
| Dennis Morelock * | 20 | 272.7 | 2015 | ||
| Lionel Emerson | 20 | 171.3 | 2014 | ||
| Alfred Marenco | 20 | 249.7 | 2013 | ||
| Armand Banuelos | 20 | 212.3 | 2012 | ||
| Helmut Bast | 20 | 247.0 | 2011 | ||
| Dirk Carr | 20 | 214.0 | 2010 | ||
| Gregory Hart | 20 | 210.3 | 2010 | ||
| Mark Torrence | 20 | 312.3 | 2009 | ||
| Tobias Escobar | 20 | 281.3 | 2009 | ||
| Miguel Villalobos | 20 | 252.3 | 2009 | ||
| Bruce Gump | 20 | 205.7 | 2009 | ||
| Ralph Bridges | 20 | 195.0 | 2007 | ||
| Gregory Hart | 20 | 287.0 | 2005 | ||
| Marcelo Depaz | 20 | 272.0 | 2005 | ||
| Joseph Seybert | 20 | 189.3 | 2000 | ||
| 69. | Aimon Gonzalez | 19 | 183.0 | 2029 | |
| Harry Bruckner | 19 | 230.0 | 2028 | ||
| Jim Ketcham | 19 | 222.0 | 2028 | ||
| Carlos Horizon | 19 | 286.7 | 2027 | ||
| Chris Beamish | 19 | 217.7 | 2027 | ||
| Alex Hulse | 19 | 212.7 | 2027 | ||
| Constantino Figuera | 19 | 176.3 | 2027 | ||
| Chris Beamish | 19 | 231.3 | 2026 | ||
| Benito Oliveira | 19 | 212.7 | 2025 | ||
| Willie Wilson | 19 | 238.3 | 2022 | ||
| Robert Silvera | 19 | 213.0 | 2022 | ||
| Patrido Pabtojas | 19 | 195.7 | 2022 | ||
| Charlie Hester | 19 | 290.0 | 2021 | ||
| Christopher Steelman | 19 | 216.7 | 2021 | ||
| Michael Errol | 19 | 181.7 | 2021 | ||
| John Andujar | 19 | 232.3 | 2020 | ||
| Charlie Hester | 19 | 280.0 | 2019 | ||
| Paul Hall | 19 | 221.7 | 2019 | ||
| Robert Echague | 19 | 214.7 | 2019 | ||
| Maddox Belcher | 19 | 166.7 | 2019 | ||
| Thomas Gabbedon | 19 | 237.7 | 2018 | ||
| Kazuma Sen | 19 | 233.3 | 2018 | ||
| Emeril Loux | 19 | 237.3 | 2017 | ||
| Jose Altamirano | 19 | 221.3 | 2017 | ||
| Walter Piccirillo | 19 | 199.7 | 2017 | ||
| Earl Boucher | 19 | 244.0 | 2016 | ||
| Walter Piccirillo | 19 | 175.3 | 2016 | ||
| Galon Thrace | 19 | 258.3 | 2015 | ||
| Robert Harris | 19 | 177.7 | 2014 | ||
| Mario Bloodworth | 19 | 169.3 | 2013 | ||
| Christopher Paladino | 19 | 209.7 | 2012 | ||
| Gary Martin | 19 | 140.7 | 2012 |
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