Originally all versions of it described sitting ducks (6)
I believe the answer is:
avoids
'ducks' is the definition.
(duck can mean to avoid)
'originally all versions of it described sitting' is the wordplay.
'originally' suggests taking the first letters.
The first letters of 'all versions of it described sitting' is 'AVOIDS'.
(Other definitions for avoids that I've seen before include "Keeps away or refrains from" , "Ducks (out of)" , "Shuns, keeps away from" , "Escapes" , "Steers clear of, dodges" .)