Young creature perpetually restricted by obstruction (7)
I believe the answer is:
leveret
'young creature' is the definition.
(I've seen this before)
'perpetually restricted by obstruction' is the wordplay.
'perpetually' becomes 'ever' (I've seen this in another clue).
'restricted by' is an insertion indicator (inserted letters are restricted or trapped).
'obstruction' becomes 'let' (let can mean a hindrance).
'ever' going within 'let' is 'LEVERET'.
(Other definitions for leveret that I've seen before include "Young animal" , "hare about in spring" , "Hare under a year old" , "Young runner" , "Young hare" .)