Beer without head: that is disturbing (5)
I believe the answer is:
eerie
'disturbing' is the definition.
'beer without head that is' is the wordplay.
'without head' means to remove the first letter.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'beer' with its initial letter taken away is 'eer'.
'eer'+'ie'='EERIE'
(Other definitions for eerie that I've seen before include "Scary, weird" , "Spooky, macabre" , "Mysterious" , "Unnatural" , "spine-chilling" .)