Protect a railway employee (5)
I believe the answer is:
guard
'protect' is the definition.
(guarding is a kind of protecting)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for guard that I've seen before include "Custodian" , "Protect(or)" , "Police" , "Sentry" , "Screw" .)