| Abbreviation | Definition |
|---|---|
| ACO | American Cornhole Organization |
| ACOB | Athletic College Old Boys |
| ACOS | Australian Centre for Olympic Studies |
| ACPRC | Australian Conference of Principal Race Clubs |
| ACR | ACRoss |
| ACR | American Club Racer |
| ACR | American Club Racing |
| ACR | Automotive Club Racer |
| ACR | Average Crappy Racecar |
| ACRD | Assassination City Roller Derby |
| ACRG | Alamo City RollerGirls (roller derby) |
| ACRP | American Curl Rescue Project |
| ACS | Acmlm Championship Series |
| ACS | All Can Swim |
| ACS | Anti-Chop System |
| ACS | Automatic Championship System |
| ACSA | Armenian Churches Sports Association |
| ACSL | Austrian College Sports League |
| ACTJRU | Australian Capital Territory Junior Rugby Union |
| ACTL | Auto Cross Team Lievelde |