Butchers giggling in sports clothing (10)
I believe the answer is:
slaughters
'butchers' is the definition.
(I know this)
'giggling in sports clothing' is the wordplay.
'giggling' becomes 'laughter'.
'in' means one lot of letters goes inside another.
'clothing' says to hollow out the word (remove centre letters).
'sports' with its centre removed is 'ss'.
'laughter' placed into 'ss' is 'SLAUGHTERS'.
(Other definitions for slaughters that I've seen before include "Kills" , "Dispatches" .)