Bear decapitated in destruction (4)
I believe the answer is:
ruin
'destruction' is the definition.
(ruin is a kind of destruction)
'bear decapitated' is the wordplay.
'bear' becomes 'bruin' (term for a bear in children's stories).
'decapitated' means to remove the first letter.
'bruin' with its initial letter taken off is 'RUIN'.
'in' is the link.
(Other definitions for ruin that I've seen before include "Total disaster" , "Destory or bankrupt" , "fall" , "dishonour" , "Dilapidated building" .)