Football referees
Oscar Moncada
Oliver Moran
Orxan Məmmədov
Odeh Na'al
Ori Nakel
Oshane Nation
Ola Nielsen
Ola Hobber Nilsen
Oskar Nilsson
O. Noonan
Olvin Oliva
Oleh Olkhovskyi
Oleksandr Omelchenko
Omar Oporto
Omar Alejandro Ortega García
Özer Özden
Onur Özütoprak
Onur Özütoprak
Ömər Paşayev
Oleksandr Pavlyuk
Ondřej Pechanec
O. Pelikán
Osvaldas Pliuškys
Omar Andrés Ponce Manzo
Orlando Quintana
Olani Qwinda
Oliver Raudsepp
Oliver Reitala
Olatz Rivera Olmedo
Ovidiu Robu
Oskar Roeck
Óscar Rojas
Oleksandr Sakhno
Omar Sallah
Ole Andreas Schulz
Onur Sekman
Özgür Sevinç
Oleksandr Shandor
Oliver Skaret Barsøe
Ole Andreas Skogsrud Haukåsen
Oleg Snegirev
Olsi Sokoli
Oleg Sokolov
Oleksandr Solovyan
Oleg Stoianov
Oktay Taş
Olga Tereshko
O. P Thakur
Olivier Thual
Olivia Tschon