Where solver can find a castle's boundary! (4)
I believe the answer is:
four
'boundary' is the definition.
(type of score in cricket)
'where solver can find a castle's' is the wordplay.
I cannot quite understand how this works, but
'castle' could be 'r' (abbreviation for rook/castle in chess) and 'r' is present in the answer.
The remaining letters 'fou' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for four that I've seen before include "Number of players in a doubles game" , "Rowing boat; number" , "How many Horsemen of the Apocalypse?" , "Figure" , "Cardinal" .)