Nasty riot in southeast leading to soldiers’ sudden sally (6)
I believe the answer is:
sortie
'soldiers' sudden sally' is the definition.
(a sortie is a military attack)
'nasty riot in southeast' is the wordplay.
'nasty' indicates an anagram (a nasty or wrong spelling).
'in' indicates putting letters inside.
'southeast' becomes 'SE' (synonyms).
'riot' with letters rearranged gives 'orti'.
'orti' put within 'se' is 'SORTIE'.
'leading to' is the link.
(Other definitions for sortie that I've seen before include "Offensive" , "Operational flight by a bomber or fighter" , "Sally" , "(Siege) breakout" , "Military raid" .)