Went on horseback before old cowboy show? (5)
I believe the answer is:
rodeo
'cowboy show?' is the definition.
(I've seen this before)
'went on horseback before old' is the wordplay.
'went on horseback' becomes 'rode' (I've seen this before).
'before' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'rode'+'o'='RODEO'
(Other definitions for rodeo that I've seen before include "Wild West show" , "Cowboy event" , "display of cowboy skill" , "show with mounting excitement" , "One should be up for this event" .)