Try this outside suit (6)
I believe the answer is:
hearts
'suit' is the definition.
(I've seen this before)
'try this outside' is the wordplay.
'try' becomes 'hear' (as in to try someone in court or hear their case**).
'outside' means to remove the middle letters.
'this' with its centre taken out is 'ts'.
'hear'+'ts'='HEARTS'
(Other definitions for hearts that I've seen before include "not clubs" , "Playing-card suit" , "Suit in pack" , "Cores" , "Central parts" .)