| Abbreviation | Definition |
|---|---|
| ATL | Atlanta Braves |
| ATLAS | Academics Technology Lifeskills Arts And Sports |
| ATLUTKD | Atlanta's United Tae Kwon Do |
| ATP | American Tennis Promotion |
| ATP | Anonymous Tennis Players |
| ATP | Association of Tennis Professionals |
| ATR | Australian Tournament Rankings |
| ATR | Automatic Ticket Resolution |
| ATS | Against The Spread |
| ATTAC | Advanced Tradewars, Tactical Assault And Conquer |
| ATTF | African Table Tennis Federation |
| ATTT | Agence Technique des Transports Terrestres |
| ATWE | Around the Tropic World Expedition |
| ATZ | Aeobic Training Zone |
| ATZ1 | Aerobic Training Zone 1 |
| ATZ2 | Aerobic Training Zone 2 |
| AU | Athletic Union |
| AUBB | Aurora University BaseBall |
| AUBC | Aberdeen University Basketball Club |
| AUBC | Asian University Basketball Championships |