Mistakes made by brats wasting time (6)
I believe the answer is:
errors
'mistakes' is the definition.
('error' can be a synonym of 'mistake')
'brats wasting time' is the wordplay.
'brats' becomes 'terrors' ('terror' can be a synonym of 'brat').
'wasting' suggests deleting specific letters.
'time' becomes 't' (abbreviation).
'terrors' with 't' removed is 'ERRORS'.
'made by' acts as a link.
(Other definitions for errors that I've seen before include "Mistakes, blunders" , "The Comedy of - (WS)" , "Fallacies, mistakes" , "Subject of Shakespearean 6" , "Mistakes and omissions" .)