Decent reason for play area (10)
I believe the answer is:
fairground
'play area' is the definition.
(entertainment area)
'decent reason' is the wordplay.
'decent' becomes 'fair' (I've seen this before).
'reason' becomes 'ground' (synonyms).
'fair'+'ground'='FAIRGROUND'
'for' acts as a link.
(Other definitions for fairground that I've seen before include "Scary ride here perhaps" , "Where one plays" , "Entertainment centre" , "rides here" , "Entertainment venue" .)