Exaggerated about jumpy cadet (9)
I believe the answer is:
overacted
'exaggerated' is the definition.
(I've seen this before)
'about jumpy cadet' is the wordplay.
'about' becomes 'over' (both can mean around).
'jumpy' is an anagram indicator (letters jumping around).
'cadet' with letters rearranged gives 'acted'.
'over'+'acted'='OVERACTED'
(Other definitions for overacted that I've seen before include "Piled it on" , "Exaggerated" , "Ranted on stage" , "Overdid the performance" .)