Strong criticism from the leaders of Fleet, Long and Keen (4)
I believe the answer is:
flak
'strong criticism' is the definition.
(I've seen this before)
'the leaders of fleet long and keen' is the wordplay.
'the leaders of' says to take the initial letters.
The initial letters of 'fleet long and keen' is 'FLAK'.
'from' is the link.
(Other definitions for flak that I've seen before include "Ground-to-air attack: verbal abuse" , "Severe criticism" , "Unfriendly criticism" , "Criticism (colloq.)" , "Anti-aircraft fire - strong criticism" .)