Irritable youth leader on trial (5)
I believe the answer is:
testy
'irritable' is the definition.
(testy can mean irritable or annoyed)
'youth leader on trial' is the wordplay.
'youth leader' becomes 'y' (I've seen this in other clues).
'on' says to put letters next to each other.
'trial' becomes 'test' (synonyms).
'y' put after 'test' is 'TESTY'.
(Other definitions for testy that I've seen before include "Short-tempered" , "Captious" , "Showing irritation" , "Ratty" , "snappy" .)