Strike with fear losing right old battle (5)
I believe the answer is:
alamo
'battle' is the definition.
(famous mission and siege from the Texas revolution)
'strike with fear losing right old' is the wordplay.
'strike with fear' becomes 'alarm' (I've seen this in another clue).
'losing' is a deletion indicator.
'right' becomes 'r' (common abbreviation).
'old' becomes 'o' (abbreviation).
'alarm' with 'r' removed is 'alam'.
'alam'+'o'='ALAMO'
(Other definitions for alamo that I've seen before include "The answer is a place of siege" , "Texas fort famed for defence against Mexican army" , "Famous battle in Texas launched by the Mexican army" , "ill-fated mission" , "Where Jim Bowie died" .)