Reportedly escape arrest? It’s a fallacy (15)
I believe the answer is:
misapprehension
'a fallacy' is the definition.
'reportedly escape arrest? it's' is the wordplay.
I cannot really see how this works, but
'reportedly' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
'it' could be 'sa' (old-fashioned abbreviation for sex appeal) and 'sa' is located in the answer.
This explanation may well be incorrect...
(Other definitions for misapprehension that I've seen before include "False impression" , "wrong understanding" , "Mistaken belief" .)