Severely criticise rotten cheats (6)
I believe the answer is:
scathe
'severely criticise' is the definition.
'scathe' can be an answer for 'criticise' (thesaurus). I'm unsure of the 'severely' bit.
'rotten cheats' is the wordplay.
'rotten' indicates anagramming the letters.
'cheats' is an anagram of 'SCATHE'.
Can you help me to learn more?
(Other definitions for scathe that I've seen before include "Harm, injure" , "Carpet" , "To scorn" .)