Rook in barrel to rotate (4)
I believe the answer is:
turn
'to rotate' is the definition.
(I've seen this in another clue)
'rook in barrel' is the wordplay.
'rook' becomes 'R' (chess abbreviation).
'in' is an insertion indicator.
'barrel' becomes 'tun' (tun is a kind of barrel).
'r' placed within 'tun' is 'TURN'.
(Other definitions for turn that I've seen before include "Twist; go" , "Shift - wheel - round" , "Go - short walk" , "rotation" , "Change one's mind" .)