Arrive, but not for a showdown! (4,2)
I believe the answer is:
show up
'arrive' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for show up that I've seen before include "Expose or appear as arranged" , "Arrive (for an appointment)" , "cause public embarrassment" , "Become visible" , "Expose, or arrive as expected" .)