Switch's partner (4)
I believe the answer is:
bait
'switch's partner' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bait that I've seen before include "Used to lure fish or other animals into danger" , "N in radio comms" , "Enticement for fish" , "What lures" , "Enticement, lure" .)