Regularly flout detectives, that’s clear (5)
I believe the answer is:
lucid
'clear' is the definition.
('lucid' can be similar in meaning to 'clear')
'regularly flout detectives' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'detectives' becomes 'cid' (**).
The alternating letters of 'flout' are 'lu'.
'lu'+'cid'='LUCID'
'that's' is the link.
(Other definitions for lucid that I've seen before include "Transparently clear" , "Intellectually bright" , "Easily understood; sane" , "Clearly expressed and altogether rational" , "Bright; sane" .)