Lured over hard first barrier (6)
I believe the answer is:
hurdle
'barrier' is the definition.
(I know that hurdle is a type of barrier)
'lured over hard first' is the wordplay.
'over' is an anagram indicator.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'first' says to put letters next to each other.
'lured' anagrammed gives 'urdle'.
'urdle' put after 'h' is 'HURDLE'.
(Other definitions for hurdle that I've seen before include "Light movable barrier in certain races" , "Challenge (to be cleared)" , "Barrier (to be jumped)" , "Obstacle (that needs to be overcome)" , "Vault" .)