Fresh greens I’d eat at first, given vitality (9)
I believe the answer is:
energised
'given vitality' is the definition.
'fresh greens i'd eat at first' is the wordplay.
'fresh' is an anagram indicator.
'at first' indicates taking the first letters.
The first letter of 'eat' is 'e'.
'greens'+'id'+'e'='greenside'
'greenside' with letters rearranged gives 'ENERGISED'.
(Other definitions for energised that I've seen before include "Animated" , "Roused" , "Fired up" , "Given drive" , "ready for action" .)