Over the top - that's clear (5)
I believe the answer is:
overt
'clear' is the definition.
(both can mean apparent or obvious)
'over the top' is the wordplay.
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'top' becomes 'over' (I've seen this before).
't' put after 'over' is 'OVERT'.
'that's' is the link.
(Other definitions for overt that I've seen before include "Openly displayed" , "Open and undisguised" , "Open, not 1 across" , "Explicit" , "Open and obvious" .)