First stage involves a racket (7)
I believe the answer is:
leading
'first' is the definition.
(thesaurus)
'stage involves a racket' is the wordplay.
'stage' becomes 'leg' ('leg' can be a synonym of 'stage').
'involves' means one lot of letters goes inside another.
'racket' becomes 'din' (I've seen this before).
'a'+'din'='adin'
'leg' going around 'adin' is 'LEADING'.
(Other definitions for leading that I've seen before include "Prominent" , "Foremost" , "In the chair" , "Aligned in front" , "In pole position" .)