Pastime building card-castle (4-6)

I believe the answer is:

cats-cradle

'pastime' is the definition.

'building card-castle' is the wordplay.
'building' indicates an anagram.
'card'+'castle'='cardcastle'
'cardcastle' is an anagram of 'CATS CRADLE'.

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app