Trooper's ever eager taking soldier on (9)
I believe the answer is:
persevere
'soldier on' is the definition.
(I've seen this before)
'trooper's ever eager taking' is the wordplay.
'taking' indicates the answer is hidden within the clue (the answer is carried or taken by the clue).
'PERSEVERE' can be found hidden inside 'troopers ever eager'.
(Other definitions for persevere that I've seen before include "Struggle on!" , "give it another try" , "Continue (against odds)" , "Carry on regardless" , "Keep going" .)