Great — put us up before rep stands (5)
I believe the answer is:
super
'great' is the definition.
(both can mean excellent)
'us up before rep stands' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'before' is a charade indicator (letters next to each other).
'stands' is a reversal indicator (I've seen 'standing' mean this (in a down clue, letters stand up)).
'us' back-to-front is 'su'.
'rep' backwards is 'per'.
'su'+'per'='SUPER'
'put' is the link.
(Other definitions for super that I've seen before include "senior cop" , "Excellent - small-part actor" , "Prefix meaning over or extremely" , "Marvellous, terrific" , "Gushily great, excellent" .)