In contrast, it changes tack (6)
I believe the answer is:
stitch
'tack' is the definition.
(I know that tack is a more specific form of the action stitch)
'in contrast it changes' is the wordplay.
'in' says the answer is hidden in the clue.
'STITCH' is hidden in the letters of 'contrast it changes'.
(Other definitions for stitch that I've seen before include "Sew with thread" , "Pain for runner" , "For example, back" , "Sharp spasm of pain in the side" , "One in time is said to save nine" .)