They may take the field an hour before midday (6)
I believe the answer is:
eleven
'they may take the field an hour' is the definition.
The definition suggests an adverb but the answer is not.
'before midday' is the wordplay.
'before' becomes 'e' (I've seen this in other clues).
'midday' becomes 'leven' (I can't explain this - if you can you should believe this answer much more).
'e'+'leven'='ELEVEN'
Can you help me to learn more?
(Other definitions for eleven that I've seen before include "Cardinal" , "sports team?" , "Number, on a team perhaps" , "Number of pipers piping" , "Enough for a soccer side" .)