Friendly co-fighter, after poor start (5)
I believe the answer is:
pally
'friendly' is the definition.
(similar in meaning)
'co-fighter after poor start' is the wordplay.
'co-fighter' becomes 'ally' (e.g. during a war).
'after' says to put letters next to each other.
'start' indicates taking the first letters.
The first letter of 'poor' is 'p'.
'ally' put after 'p' is 'PALLY'.
(Other definitions for pally that I've seen before include "Chummy" , "On friendly terms" , "Intimate" , "China may be so" , "Close, friendly" .)