Standard-bearer taking stones to Welsh river (9)
I believe the answer is:
flagstaff
'standard-bearer' is the definition.
(I've seen this before)
'stones to welsh river' is the wordplay.
'stones' becomes 'flags' (flag is a kind of stone).
'to welsh river' becomes 'taff' (I've seen this before).
'flags'+'taff'='FLAGSTAFF'
'taking' is the link.
(Other definitions for flagstaff that I've seen before include "Jack may be seen here" , "Flying Pole" , "Arizona community" , "where colours seen" , "Pole for the standard" .)