Baseball
O
- O'Connor Pat
- O'Dowd Dan
- O'Leary Troy
- O'Neill Paul
- O'Sullivan Kevin
- Oates Johnny
- Oates Johny
- Obama Barack
- Odelin Vicyohandri
- Oeltjen Trent
- Offerman Jose
- Ogasawara Michihiro
- Ogea Chad
- Ogle Tyler
- Oh Sadaharu
- Ojeda Augie
- Olerud John
- Olivier John
- Olivio Miguel
- Oquendo Jose
- Ordonez Magglio
- Ortiz David
- Ortiz Ramon
- Ortiz Russ
- Orza Gene
- Oswalt Roy
- Ottavino Adam
- Owen Faylene
- Owings Micah