Reporting to Cardinal Newman, umpteen leaders upset (5)
I believe the answer is:
under
'reporting to' is the definition.
'cardinal newman umpteen leaders upset' is the wordplay.
'cardinal' becomes 'red' (I've seen this in other clues**).
'leaders' suggests taking the first letters.
'upset' shows that the letters should be reversed in order.
The first letters of 'newman umpteen' is 'nu'.
'red'+'nu'='rednu'
'rednu' reversed gives 'UNDER'.
(Other definitions for under that I've seen before include "See 7" , "Managed by" , "Covered" , "Subject to the authority of" , "Lower than" .)