Railed audibly as trespassers do (6)
I believe the answer is:
invade
'railed audibly as trespassers do' is the definition.
I can't tell whether this defines the answer.
'as trespassers do' is the wordplay.
'as' becomes 'in' (I've seen this in other clues).
'trespassers do' becomes 'vade' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in'+'vade'='INVADE'
Can you help me to learn more?
(Other definitions for invade that I've seen before include "Enter illegally" , "Enter with armed forces to attack" , "Penetrate other country with armed forces" , "Attack and move in" , "make unwelcome advances" .)