Trench restricts spring expedition (8)
I believe the answer is:
dispatch
'expedition' is the definition.
(I know that expedition can be written as dispatch)
'trench restricts spring' is the wordplay.
'trench' becomes 'ditch' (synonyms).
'restricts' is an insertion indicator.
'spring' becomes 'spa' (spa can mean a mineral spring).
'ditch' going around 'spa' is 'DISPATCH'.
(Other definitions for dispatch that I've seen before include "Kill, send off" , "alacrity" , "making killing" , "Communication" , "Send with speed" .)