Plain unfortunate king caught in court regularly (5-3)
I believe the answer is:
clear-cut
'plain' is the definition.
(clear-cut means plain or obvious)
'unfortunate king caught in court regularly' is the wordplay.
'unfortunate king' becomes 'Lear' (Shakespeare's King Lear).
'caught' becomes 'c' (cricket abbreviation).
'in' indicates putting letters inside.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'court' are 'cut'.
'lear'+'c'='learc'
'learc' placed into 'cut' is 'CLEAR-CUT'.
(Other definitions for clear-cut that I've seen before include "Unambiguous" , "Sharp" , "Very distinct, not open to doubt" , "Distinct and sharply-defined" , "Decisive" .)