Cheer starter (3)
I believe the answer is:
hip
'cheer starter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hip that I've seen before include "Swinging" , "Slangily trendy part of body" , "Trendy bodily joint?" , "Fruit of the wild rose (3)" , "Leg joint" .)