Battle a government leader in tribunal (9)
I believe the answer is:
agincourt
'battle' is the definition.
(Agincourt is an example)
'a government leader in tribunal' is the wordplay.
'leader' suggests taking the first letters.
'tribunal' becomes 'court' (synonyms).
The initial letter of 'government' is 'g'.
'a'+'g'+'in'+'court'='AGINCOURT'
(Other definitions for agincourt that I've seen before include "English-French battle" , "English victory in 1415" , "Battle in Hundred Years' War" , "French village" , "Battleground" .)