| Abbreviation | Definition |
|---|---|
| OAC | Olympic Athletic Club |
| OAC | On Athletics Club |
| OACA | Oregon Athletic Coaches Association |
| OACW | Ohio Athletic Conference Wrestling |
| OACWC | Ohio Athletic Conference Wrestling Championship |
| OAFC | Oldham Athletic Football Club |
| OAJ | Oregon Athletics Journal |
| OAL | Oakland Athletic League |
| OASIS | Oldham Athletic Supporters In The South |
| OCAA | Ontario Colleges Athletic Association |
| OCAC | Oklahoma Collegiate Athletic Conference |
| OCAC | Oxford City Athletic Club |
| ODAC | Old Dominion Athletic Conference |
| OFSAA | Ontario Federation of School Athletic Associations |
| OFSAA | Ontario Federation of Schools Athletic Association |
| OFSAA | Ontario Federation of Secondary Athletic Associations |
| OGA | Onigokko Grand Athletics |
| OHSA | Ohio High School Athletic Association |
| OHSAA | Ohio High School Athletic Association |
| OMAC | Old Montauk Athletic Club |