They succeeded Wrens in shake-up (7)
I believe the answer is:
winners
'they succeeded' is the definition.
(people who won or succeeded)
'wrens in shake-up' is the wordplay.
'shake up' is an anagram indicator (I've seen 'shakes up' mean this).
'wrens'+'in'='wrensin'
'wrensin' anagrammed gives 'WINNERS'.
(Other definitions for winners that I've seen before include "25 15 [GOLDMEDALLIST]s" , "Victors" .)