Run out of caustic chemical (4)
I believe the answer is:
acid
'chemical' is the definition.
(thesaurus)
'run out of caustic' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'out of' is a deletion indicator.
'caustic' becomes 'acrid' (I've seen this before).
'acrid' with 'r' removed is 'ACID'.
(Other definitions for acid that I've seen before include "Drug LSD (colloq.)" , "Corrosive fluid" , "Sour - vitriolic" , "Corrosive liquid; drug" , "Bitter or sour" .)