Hesitation to shout — not a mistake (5)
I believe the answer is:
error
'mistake' is the definition.
(I know that mistake can be written as error)
'hesitation to shout not a' is the wordplay.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'to shout' becomes 'roar' (roaring is a kind of shouting).
'not' indicates named letters should be taken away.
'roar' with 'a' taken away is 'ror'.
'er'+'ror'='ERROR'
(Other definitions for error that I've seen before include "Mistake from terrorist" , "Solecism" , "Fallacy, mistake" , "Miscalculation" , "Mistake, lapse" .)