| Player Name | Pos | Ht | Wt | B-T | BornDate | Place | HiLvl | Stat Years | MLB Years | Draft Information |
| Brian O'Bannon | OF | 5-9 | 160 | L-R | 1995-07-29 | Dallas,Texas | NCAA | 2014-2014 | - | |
| Ed O'Bannon | P | 6-7 | 226 | R-R | 1998-- | Henderson,Nevada | NCAA | 2017-2017 | - | |
| Isaac O'Bear | P | 5-11 | 180 | R-R | 1995-- | White Castle,Louisiana | NCAA | 2015-2015 | - | |
| Brent O'Berry | OF | 6-1 | 150 | L-R | 1988-09-15 | Greensboro,North Carolina | NCAA | 2008-2009 | - | |
| Jackson O'Boy | C | 5-11 | 185 | R-R | 1998-- | Aptos,California | NCAA | 2018-2018 | - | |
| Dalton O'Boyle | P | 6-2 | 212 | L-R | 1998-- | Fort Wayne,Indiana | NCAA | 2017-2018 | - | |
| Bobby O'Brien | OF | 6-2 | 200 | R-R | 1989-01-27 | Greenwich,Connecticut | NCAA | 2008-2010 | - | |
| Caden O'Brien | P | 6-1 | 190 | R-L | 1999-01-24 | Maiden,North Carolina | NCAA | 2018-2018 | - | |
| Chris O'Brien | P | 5-11 | 193 | L-L | 1991-11-23 | Drexel Hill,Pennsylvania | NCAA | 2012-2013 | - | |
| Chris O'Brien | P | - | - | NCAA | 2001-2002 | - | ||||
| Chris O'Brien | IF | 6-0 | 200 | R-R | Massapequa,New York | NCAA | 2004-2004 | - | ||
| Cody O'Brien | P | 6-0 | 202 | R-R | 1995-- | Mesa,Arizona | NCAA | 2014-2017 | - | |
| Connor O'Brien | C | 6-2 | 196 | R-R | 1995-05-27 | Seattle,Washington | NCAA | 2015-2018 | - | |
| Connor O'Brien | IF | 6-3 | 179 | R-R | - | NCAA | 2018-2018 | - | ||
| Conor O'Brien | P | 6-1 | 180 | R-R | 1993-10-09 | Tampa,Florida | NCAA | 2013-2016 | - | |
| David O'Brien | P | 6-3 | 190 | R-R | 1988-12-12 | Whitman,Massachusetts | NCAA | 2008-2011 | - | |
| Dillon O'Brien | P | 5-10 | 170 | - | Morristown,New Jersey | NCAA | 2014-2015 | - | ||
| Eric O'Brien | OF-C | 6-0 | 210 | L-R | 1990-- | Tucson,Arizona | NCAA | 2012-2013 | - | |
| Eric O'Brien | OF | 6-2 | 185 | R-R | 1979-09-24 | Cincinnati,Ohio | NCAA | 2000-2003 | - | 1996-57-1573-ARI |
| Gage O'Brien | P | 6-4 | 195 | R-R | 1996-06-15 | Branson,Missouri | NCAA | 2017-2017 | - | |
| Jake O'Brien | 1B-OF | 6-0 | 200 | L-L | 1992-09-03 | Tulsa,Oklahoma | NCAA | 2012-2015 | - | |
| Jim O'Brien | 3B-OF | 5-10 | 165 | R-R | 1985-09-05 | Hackensack,New Jersey | NCAA | 2007-2007 | - | |
| Justin O'Brien | P | 6-5 | 180 | R-R | 1990-09-12 | Montclair,New Jersey | NCAA | 2011-2011 | - | |
| Kenny O'Brien | P | 6-2 | 170 | L-L | 1991-- | Yonkers,New York | NCAA | 2010-2013 | - | |
| Kevin O'Brien | P | 6-1 | 200 | R-R | 1981-02-10 | Patterson,New York | NCAA | 2000-2003 | - | |
| Player Name | Pos | Ht | Wt | B-T | BornDate | Place | HiLvl | Stat Years | MLB Years | Draft Information |
| Kian O'Brien | IF | 5-11 | 185 | - | - | NCAA | 2018-2018 | - | ||
| Mason O'Brien | 1B-OF | 6-0 | 210 | L-L | 1996-02-01 | Owasso,Oklahoma | NCAA | 2015-2018 | - | |
| Matt O'Brien | P | 6-2 | 220 | L-L | 1986-01-24 | Hingham,Massachusetts | NCAA | 2005-2009 | - | |
| Murphy O'Brien | P | 6-1 | 185 | R-R | 1998-- | Rocky River,Ohio | NCAA | 2017-2018 | - | |
| Nick O'Brien | P | 6-3 | 190 | R-R | 1998-- | Keller,Texas | NCAA | 2017-2017 | - | |
| Patrick O'Brien | P | 6-2 | 195 | R-R | 1991-01-20 | Boardman,Ohio | NCAA | 2010-2014 | - | |
| Richard O'Brien | C | 5-11 | 199 | R-R | 1984-08-11 | Little Rock,Arkansas | NCAA | 2006-2007 | - | 2004-47-1403-CHA |
| Richie O'Brien | P | 6-3 | 190 | R-R | 1988-02-02 | Boardman,Ohio | NCAA | 2007-2010 | - | |
| Riley O'Brien | P | 6-4 | 205 | L-L | 1995-03-16 | Seattle,Washington | NCAA | 2014-2015 | - | |
| Robert O'Brien | 1B | R-R | 1976-09-08 | Arcadia,California | NCAA | 1997-1998 | - | 1994-60-1519-CLE | ||
| Sean O'Brien | P | 6-4 | 205 | L-L | 1984-04-28 | Woodland,California | NCAA | 2003-2006 | - | |
| Sean O'Brien | IF | 6-2 | 190 | R-R | 1991-07-29 | Clearwater,Florida | NCAA | 2011-2014 | - | |
| Sean O'Brien | 1B | 6-1 | 215 | L-L | 1984-12-31 | Mount Kisco,New York | NCAA | 2004-2008 | - | 2003-45-1340-MON |
| Shawn O'Brien | IF | 6-1 | 185 | R-L | 1991-- | Kennewick,Washington | NCAA | 2010-2013 | - | |
| Slater O'Brien | P | 6-5 | 205 | L-L | 1998-- | Bronx,New York | NCAA | 2018-2018 | - | |
| Tom O'Brien | P | 6-5 | 265 | L-L | 1994-- | Watertown,Connecticut | NCAA | 2013-2016 | - | |
| Trevor O'Brien | C | 5-11 | 180 | R-R | 1983-- | Cranston,Rhode Island | NCAA | 2002-2002 | - | |
| Corie O'Bryan | 3B | 5-11 | 220 | R-R | 1982-01-10 | Frederick,Maryland | NCAA | 2003-2004 | - | |
| Robbie O'Bryan | 1B | 6-2 | 235 | L-L | 1988-03-08 | Marietta,Georgia | NCAA | 2008-2010 | - | |
| Steven O'Bryant | P | 6-0 | 160 | R-R | 1992-- | Baton Rouge,Louisiana | NCAA | 2013-2015 | - | |
| Kyle Obenauf | P | 6-4 | 225 | R-R | 1983-10-27 | Salem,Wisconsin | NCAA | 2004-2006 | - | |
| Mark Obenchain | P | 6-3 | 204 | R-R | 1988-- | Henderson,Kentucky | NCAA | 2008-2009 | - | |
| Drew Ober | IF-OF | 6-2 | 195 | R-R | 1997-03-28 | Huntersville,North Carolina | NCAA | 2016-2018 | - | |
| Ryan Ober | IF | 5-11 | 180 | R-R | - | NCAA | 2018-2018 | - | ||
| Eric Oberding | P-IF | 6-5 | 218 | R-R | 1978-08-07 | West Carrollton,Ohio | NCAA | 2001-2002 | - | |
| Player Name | Pos | Ht | Wt | B-T | BornDate | Place | HiLvl | Stat Years | MLB Years | Draft Information |
| John Oberholtzer | P | 5-10 | 180 | L-L | 1993-05-01 | Stockton,California | NCAA | 2013-2014 | - | |
| Alex Oberle | P | 6-0 | 165 | R-R | 1989-- | San Jose,California | NCAA | 2010-2011 | - | |
| Wes Oberlin | IF | 6-3 | 215 | R-R | 1985-11-04 | Irvine,California | NCAA | 2005-2008 | - | |
| Preston Oberling | P | 6-2 | 185 | R-R | 1995-06-02 | Little Rock,Arkansas | NCAA | 2015-2017 | - | |
| Dan Obermeier | C | 6-0 | 168 | R-R | 1983-09-28 | Pittsburgh,Pennsylvania | NCAA | 2003-2006 | - | |
| Bobby Oberschlake | P | 6-1 | 186 | L-L | 1986-07-11 | Felicity,Ohio | NCAA | 2005-2008 | - | |
| Alex Obert | P | 6-7 | 185 | R-R | 1983-- | Charlotte,North Carolina | NCAA | 2002-2004 | - | |
| Michael Oberto | P | 6-1 | 185 | R-R | 1989-10-22 | Broomfield,Colorado | NCAA | 2010-2012 | - | |
| Ted Oberwager | IF | 6-0 | 181 | R-L | 1984-- | Bryn Mawr,Pennsylvania | NCAA | 2003-2003 | - | |
| Nic Obey | OF | 6-0 | 195 | R-L | 1988-10-25 | Chatfield,Minnesota | NCAA | 2008-2011 | - | |
| Jake Oblas | UT | 6-2 | 180 | R-R | 1998-- | Gunter,Texas | NCAA | 2017-2018 | - | |
| Pedro Obregon | IF-OF | 6-0 | 195 | R-R | 1984-12-06 | Miami,Florida | NCAA | 2004-2007 | - | |
| Mark Obszanski | P | 6-6 | 230 | R-R | 1982-09-03 | Munster,Indiana | NCAA | 2005-2006 | - | |
| Michael Obuchowski | OF | 6-0 | 185 | L-L | 1985-12-01 | Lebanon,New Hampshire | NCAA | 2006-2009 | - | |
| Luke Obukowicz | P | 6-1 | 195 | R-R | 1986-06-18 | Kirkwood,Missouri | NCAA | 2006-2007 | - | |
| Michael Obyc | OF | 6-0 | 187 | R-R | 1985-10-10 | Columbus,Ohio | NCAA | 2005-2008 | - |
