Guard lost head at way in (5)
I believe the answer is:
entry
'way in' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for entry that I've seen before include "Competitor" , "Door; appearance" , "candidate" , "Admission" , "Record - number of contestants" .)