Leader of armed mob almost seizing city in battle (5)
I believe the answer is:
alamo
'battle' is the definition.
(famous mission and siege from the Texas revolution)
'leader of armed mob almost seizing city' is the wordplay.
'leader of' suggests taking the first letters.
'almost' means to remove the last letter (most of the word but not all of it).
'seizing' is an insertion indicator.
'city' becomes 'la' (Los Angeles).
The first letter of 'armed' is 'a'.
'mob' with its last letter removed is 'mo'.
'a'+'mo'='amo'
'amo' enclosing 'la' is 'ALAMO'.
'in' is the link.
(Other definitions for alamo that I've seen before include "Texas mission besieged and captured by Mexican forces in 1836" , "Mission building in Texas, site of famous siege by Mexico" , "Site of a Texas siege, 1836" , "Texas fort, scene of famous siege by Mexican army" , "Texas mission taken by Mexican forces in 1836" .)