The Irish Open Softball Tournament (known as IOST) is the highlight of the softball calendar in Ireland. This tournament sees a large number of teams congregate in Limerick for two days of softball, fun and social antics. Team registration for the Brian Walshe Cup opens up early each year (owing to its popularity), with details advertised on the Softball Ireland website and social media pages.
Past IOST Winners
| Year | Venue | Winner | Runner Up |
| 2025 | University of Limerick | ||
| 2024 | MTU Cork | Belfast Cubs | Belfast Softball Club |
| 2023 | MTU Cork | Belfast Softball Club | Ori-ginals |
| 2022 | MTU Cork | BatPak | Traiderz |
| 2021 | ALSAA (1 Day) | TNT | TBC |
| 2020 | Not Held Due to Covid | N/A | N/A |
| 2019 | University of Limerick | Dodder | Sons of Pitches |
| 2018 | University of Limerick | Originals | Dodder |
| 2017 | Carlow IT | TNT | Marlay |
| 2016 | University of Limerick | Marlay | Dodder Dynamoes |
| 2015 | University of Limerick | Originals | 2Pak |
| 2014 | University of Limerick | Originals | Dodder Dynamoes |
| 2013 | University of Limerick | Originals | Dodder Dynamoes |
| 2012 | University of Limerick | Stingers* | Originals |
| 2011 | University of Limerick | Dodder Dynamoes | Originals |
| 2010 | Cork IT | Marlay Martyrs | Stingers* |
| 2009 | Cork IT | Oddsox Green | Stingers* |
| 2008 | University of Ulster | BatPak | Stingers* |
| 2007 | University of Limerick | Oddsox Green | BatPak |
| 2006 | University of Limerick | BatPak | Stingers* |
| 2005 | University of Limerick | BatPak | |
| 2004 | London Breakers* | ||
| 2003 | Oddsox Green | ||
| 2002 | ? | ||
| 2001 | Saints Stingers* | ||
| 2000 | Dodder Dynamoes | ||
| 1999 | Oddsox | ||
| 1998 | Warpak | ||
| 1997 | Batpak | ||
| 1996 | Marlay Martyrs |