Muster that's circular and rising (5-2)
I believe the answer is:
'muster' is the definition.
'circular and rising' is the wordplay.
'circular' becomes 'round' (synonyms).
'and' is a charade indicator (letters next to each other).
'rising' becomes 'up' (similar in meaning).
'that's' is the link.
(Another definition for round-up that I've seen is "Summary of events".)