Middle of state hit by old battle (5)
I believe the answer is:
Here is my best explanation:
'battle' is the definition.
(famous mission and siege from the Texas revolution)
'middle of state hit by old' is the wordplay.
'middle of' says to take the centre.
'hit' becomes 'lam' (to 'lam' means to hit hard).
'by' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
The middle letter of 'state' is 'a'.
(Other definitions for alamo that I've seen before include "historical Franciscan mission", "Site of famous battle in Texas", "Texas fort, scene of famous siege by Mexican army", "Texas site of 1836 siege", "Massacre scene in Texas", "Davy Crockett's last stand", "Texas fort famed for defence against Mexican army", "The answer is a place of siege", "Site of famous siege" and "Site of 1836 massacre in Texas".)