Mad lad gets poor mare frightened (7)
I believe the answer is:
alarmed
'frightened' is the definition.
(alarming is a kind of frightening)
'mad lad gets poor mare' is the wordplay.
'mad' is an anagram indicator.
'gets' means one lot of letters goes inside another (gets can mean captures or absorbs).
'poor' indicates an anagram.
'lad' with letters rearranged gives 'ald'.
'mare' with letters rearranged gives 'arme'.
'ald' going around 'arme' is 'ALARMED'.
(Other definitions for alarmed that I've seen before include "Frightened, scared" , "Experiencing a sudden sense of danger" , "Worried" , "Given a turn" , "like Icarus as wax melted?" .)