| Abbreviation | Definition |
|---|---|
| MRBC | Missouri River Boat Club |
| MRBC | Muskegon River Boat Club |
| MRC | Melbourne Racing Club |
| MRCC | Media Research Club of Chicago |
| MRCP | Mini Racing Club Pilatus |
| MRFC | Medway Rugby Football Club |
| MRFC | Melbourne Rugby Football Club |
| MRFC | Moseley Rugby Football Club |
| MRFC | Mt Rainier Futbol Club |
| MRFC | Muscat Rugby Football Club |
| MRPC | Meade Rifle and Pistol Club |
| MRPC | Medford Rifle Pistol Club |
| MRRC | Mad River Radio Club |
| MRRC | Mystic River Rugby Club |
| MRSC | Millennium Running Social Club |
| MRSC | Munster Rugby Supporters Club |
| MSBC | Mahen Smash Badminton Club |
| MSBC | Miracle Strip Bass Club |
| MSC | Moonlighting Social Club |
| MSCC | Martin Sports Car Club |