To commit it one rats by design (7)
I believe the answer is:
treason
'to commit it' is the definition.
I can't tell whether this definition defines the answer.
'one rats by design' is the wordplay.
'by' is a charade indicator (letters next to each other).
'design' is an anagram indicator.
'one' put after 'rats' is 'ratsone'.
'ratsone' with letters rearranged gives 'TREASON'.
Can you help me to learn more?
(Other definitions for treason that I've seen before include "Gunpowder Plot, say" , "Crime of disloyalty" , "Disloyalty (to one's country)" , "Criminal attempt to overthrow a government" , "Betrayal of one's nation" .)