Mud, it's spread across a sports ground (7)
I believe the answer is:
stadium
'sports ground' is the definition.
(I've seen this before)
'mud it's spread across a' is the wordplay.
'spread' is an anagram indicator.
'across' means one lot of letters goes inside another.
'mud'+'its'='mudits'
'mudits' is an anagram of 'stdium'.
'stdium' placed around 'a' is 'STADIUM'.
(Other definitions for stadium that I've seen before include "bowl?" , "Sports arena" , "eg Yankee, Wembley" , "Venue for sporting events, concerts etc" , "A major sports ground" .)