During effort comes across cooler soldiers (8)
I believe the answer is:
infantry
'soldiers' is the definition.
(I've seen this before)
'during effort comes across cooler' is the wordplay.
'during' becomes 'in' (I've seen this in other clues).
'effort' becomes 'try' ('try' can be a synonym of 'effort'**).
'comes across' is an insertion indicator.
'cooler' becomes 'fan' (I've seen this before).
'in'+'try'='intry'
'intry' enclosing 'fan' is 'INFANTRY'.
(Other definitions for infantry that I've seen before include "part of the army" , "Grunts" , "Army unit of foot soldiers" , "Unmounted fighters" , "Foot-soldiers" .)