Player securing fine wicket — a declaration may follow it (3,2,3)

'declaration may follow it' is the definition.
(a declaration of war might follow an act of war)

'player securing fine wicket a' is the wordplay.
'player' becomes 'actor' (synonyms).
'securing' indicates putting letters inside.
'fine' becomes 'f' (abbreviation).
'wicket' becomes 'w'.
'f'+'w'+'a'='fwa'
'actor' placed around 'fwa' is 'ACT OF WAR'.