Chose to upset the top man (5)
I believe the answer is:
opted
'chose' is the definition.
(I've seen this before)
'upset the top man' is the wordplay.
'upset' indicates anagramming the letters.
'man' becomes 'ed' (short for edward).
'top' is an anagram of 'opt'.
'opt'+'ed'='OPTED'
'to' acts as a link.
(Other definitions for opted that I've seen before include "Depot (anag.)" , "Made choice, selected" , "Decided as in 10 Across" , "Chosen - elected" , "Chose from depot" .)