Clue: Medic stops team leaders from buying extra drink (6)
Answer: IMBIBE
Explanation: Definition: drink
 MB(abbrev. for "Medicinae Baccalaureus", a doctor/a medic) **contained in**(stops) II(or 11/eleven, with the respective Roman numeral substitutions, a sports team of 11 players, as with a cricket team, say) + **1st letters, respectively, of**(leaders from) "buying extra".
Defn: To ….