Regularly seen wearing Lycra -- possibly an offence! (7)
I believe the answer is:
larceny
'an offence' is the definition.
(I've seen this before)
'regularly seen wearing lycra possibly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'wearing' is an insertion indicator.
'possibly' is an anagram indicator.
The alternate letters of 'seen' are 'en'.
'lycra' anagrammed gives 'larcy'.
'en' placed into 'larcy' is 'LARCENY'.
(Other definitions for larceny that I've seen before include "Theft of personal property" , "Criminal activity" , "Stealing - theft" , "Robbery" , "crime" .)