Presenter short, so had to show up (4)
I believe the answer is:
host
'presenter' is the definition.
(as in the host of a TV show)
'short so had to show up' is the wordplay.
'to show' says the answer is hidden in the clue.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'tsoh' is hidden within 'short so had'.
'tsoh' written backwards gives 'HOST'.
(Other definitions for host that I've seen before include "Does he invite a large number?" , "Compre" , "This man entertains" , "A load" , "Crowd-entertainer" .)