Striking is back, restricting a large hospital department (7)
I believe the answer is:
salient
'striking' is the definition.
(I know that striking can be written as salient)
'is back restricting a large hospital department' is the wordplay.
'back' says the letters should be written in reverse.
'restricting' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'hospital department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'is' backwards is 'si'.
'a'+'l'='al'
'si' placed around 'al' is 'sali'.
'sali'+'ent'='SALIENT'
(Other definitions for salient that I've seen before include "Entails being most noticeable" , "obvious" , "Conspicuous; pointing outwards" , "defence work" , "part of defences" .)