Appear on horseback following display (4,2)
I believe the answer is:
show up
'appear' is the definition.
(showing up is a kind of appearing)
'on horseback following display' is the wordplay.
'on horseback' becomes 'up' (up can mean up on a horse).
'following' says to put letters next to each other.
'display' becomes 'show' (synonyms).
'up' put after 'show' is 'SHOW UP'.
(Other definitions for show up that I've seen before include "Make an appearance" , "cause public embarrassment" , "Arrive (for an appointment)" , "Expose, or arrive as expected" , "Arrive - put to shame" .)