Excessively keen initially, excellent leader of men prepared to shoot (4,3)
I believe the answer is:
took aim
'prepared to shoot' is the definition.
(I've seen this before)
'excessively keen initially excellent leader of men' is the wordplay.
'excessively' becomes 'too' ('too' can be a synonym of 'excessively').
'initially' suggests taking the first letters.
'excellent' becomes 'ai'.
'leader of' says to take the initial letters.
The initial letter of 'keen' is 'k'.
The first letter of 'men' is 'm'.
'too'+'k'+'ai'+'m'='TOOK AIM'
(Other definitions for took aim that I've seen before include "Prepared to shoot" , "Pointed towards" , "Pointed weapon (at target)" , "Lined up" .)