I left American soldier in pub not making sense (9)
I believe the answer is:
illogical
'not making sense' is the definition.
(something illogical doesn't make sense)
'i left american soldier in pub' is the wordplay.
'left' becomes 'l' (common abbreviation).
'american soldier' becomes 'GI' (informal term for a US soldier).
'in' means one lot of letters goes inside another.
'pub' becomes 'local' (one's local pub).
'gi' put into 'local' is 'logical'.
'i'+'l'+'logical'='ILLOGICAL'
(Other definitions for illogical that I've seen before include "lacking sense" , "Irrational" , "Unsound" , "Without reason" , "not following" .)