Small, fast runner always obstructed by obstacle (7)
I believe the answer is:
leveret
'small fast runner' is the definition.
'leveret' can be an answer for 'runner' (I have seen 'Young runner' mean 'leveret' so perhaps 'runner' could also mean 'leveret'). I'm unsure of the 'small fast' bit.
'always obstructed by obstacle' is the wordplay.
I cannot really understand how this works, but
'always' could be 'ever' (synonyms) and 'ever' is found within the answer.
'obstacle' could be 'let' ('let' could historically mean an obstruction) and 'let' is present in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for leveret that I've seen before include "Baby hare" , "Hare in its first year" , "Small hopper" , "Young animal" , "Young creature" .)