Ground to dig out of drainage works (5)
I believe the answer is:
arena
'ground' is the definition.
(I've seen this before)
'dig out of drainage works' is the wordplay.
'out of' indicates named letters should be taken away ('out of' can mean no longer having).
'works' indicates an anagram (letters worked into a new form).
'drainage' with 'dig' removed is 'ranae'.
'ranae' anagrammed gives 'ARENA'.
'to' acts as a link.
(Other definitions for arena that I've seen before include "Field of conflict" , "Wembley, for example" , "Field of combat" , "Playing area" , "Gladiatorial ring" .)