Messengers climbing, but not winning! (7-2)
I believe the answer is:
runners-up
'messengers' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps there's a link between them I don't understand?
'climbing but not winning' is the wordplay.
I cannot quite see how this works, but
'climbing' could be 'up' and 'up' is found in the answer.
'not' could be 'un' (I've seen this in other clues) and 'un' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for runners-up that I've seen before include "Those not quite winning" , "Those who come second" , "Silver medallists" , "Second-placed competitors" , "Those behind the winner" .)