Touch on the shoulder (3)
I believe the answer is:
tap
'touch on the shoulder' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tap that I've seen before include "Light touch (hot or cold?)" , "Dancing" , "that's less hard than 11 [BASH] or 22 [BATTER]" , "Strike lightly" , "Flow controller; knock" .)