Players: last names starting with O
64 players, with the number of cards for each.
- Riley O'Brien 8
- Caroline O'Connor 7
- Ethan O'Donnell 1
- Lefty O'Doul 1
- Griff O'Ferrall 11
- Connor O'Halloran 4
- Ryan O'Hearn 20
- Logan O'Hoppe 123
- Brian O'Keefe 2
- Jack O'Loughlin 3
- Paul O'Neill 54
- Tyler O'Neill 48
- Bailey Ober 23
- Cade Obermueller 6
- Christian Montes De Oca 5
- Yoiber Ocopio 1
- Rougned Odor 6
- Jake Odorizzi 4
- Shinnosuke Ogasawara 15
- Sadaharu Oh 20
- Pierson Ohl 2
- Shohei Ohtani 1571
- Kazuma Okamoto 108
- Chris Okey 2
- Peyton Olejnik 1
- Tony Oliva 36
- Edward Olivares 5
- Al Oliver 2
- Michael Oliveto 7
- Adam Oller 3
- Emmett Olson 2
- Matt Olson 525
- Reese Olson 41
- Christian Oppor 1
- Magglio Ordonez 12
- Jonathan Ornelas 17
- Tirso Ornelas 6
- Maikol Orozco 1
- Don Orsillo 7
- Rafael Ortega 3
- Abimelec Ortiz 12
- Capri Ortiz 6
- D'Angelo Ortiz 6
- David Ortiz 512
- Deniel Ortiz 6
- Joey Ortiz 51
- Luis Ortiz 20
- Eric Orze 3
- Oswaldo Osorio 1
- Erik Ostberg 1
- Alejandro Osuna 9
- Michel Otañez 3
- Amos Otis 5
- Mel Ott 41
- Adam Ottavino 7
- James Outman 101
- Alexander Ovalles 1
- Austin Overn 7
- Johan Oviedo 9
- Hunter Owen 1
- Josh Owens 9
- Tyler Owens 4
- Avery Owusu-Asiedu 5
- Marcell Ozuna 89