- O'Brien, Patrick
- O'Donnell, Neil
- O'Donnell, Sean
- O'Hara, Shaun
- O'Leary, George
- O'Leary, Troy
- O'Malley, Peter
- O'Meara, Mark
- O'Neal, Deltha
- O'Neal, Jermaine
- O'Neal, Shaquille
- O'Neill, Ann
- O'Neill, Jeff
- O'Neill, Joe
- O'Neill, Kevin
- O'Neill, Paul
- O'Neill, Tim
- Oakley, Charles
- Oates, Adam
- Oben, Roman
- Ochoa, Lorena
- Odelein, Lyle
- Odom, Lamar
- Oelhoffen, Kimo von
- Offerman, Jose
- Ogden, Jonathan
- Ogilvie, Joe
- Ogrin, David
- Ogunleye, Adewale
- Ohlund, Mattias
- Ohman, Will
- Ojeda, Augie
- Okafor, Emeka
- Okeafor, Chike
- Okposo, Kyle
- Okur, Mehmet
- Olajuwon, Hakeem
- Olerud, John
- Oliver, Darren
- Oliver, David
- Ollie, Kevin
- Olowokandi, Michael
- Olsen, Ben
- Olsen, Eric
- Olsen, Greg
- Olsen, Merlin
- Olson, Erik
- Ordonez, Magglio
- Ordonez, Rey
- Orlovsky, Dan
- Orosco, Jesse
- Ortiz, David
- Ortiz, Russ
- Orton, Kyle
- Osgood, Chris
- Osik, Keith
- Oswalt, Roy
- Ott, Mel
- Outlaw, Bo
- Owen, Steve
- Owens, Billy
- Owens, Eric
- Owens, Jerry
- Owens, Terrell
- Ozaki, Joe
- Ozuna, Pablo