Weird thing following everybody when it gets dark (9)
I believe the answer is:
nightfall
'when it gets dark' is the definition.
'weird thing following everybody' is the wordplay.
'weird' is an anagram indicator.
'following' becomes 'f' (used when citing page numbers etc).
'everybody' becomes 'all' (all people).
'thing' is an anagram of 'night'.
'night'+'f'+'all'='NIGHTFALL'
(Other definitions for nightfall that I've seen before include "when the light fails" , "The onset of darkness" , "gloaming" , "End of day" , "Arrival of darkness" .)