Succeeded entering stadium, left side (7)
I believe the answer is:
arsenal
'side' is the definition.
(English football club or side)
'succeeded entering stadium left' is the wordplay.
'succeeded' becomes 's' (genealogical abbreviation).
'entering' is an insertion indicator.
'stadium' becomes 'arena' (eg a sports arena).
'left' becomes 'l' (common abbreviation).
's' placed inside 'arena' is 'arsena'.
'arsena'+'l'='ARSENAL'
(Other definitions for arsenal that I've seen before include "English football club and military depot" , "munitions factory" , "Collection of weapons" , "Place where guns and ammunition are stored" , "Munitions store and English football team" .)