Provoke troublesome bearcat in river (10)
I believe the answer is:
exacerbate
'provoke' is the definition.
(I've seen this before)
'troublesome bearcat in river' is the wordplay.
'troublesome' indicates anagramming the letters.
'in' indicates putting letters inside.
'river' becomes 'exe' (I've seen this before).
'bearcat' with letters rearranged gives 'acerbat'.
'acerbat' placed within 'exe' is 'EXACERBATE'.
(Other definitions for exacerbate that I've seen before include "Worsen" , "Provoke" , "Make (a bad thing) worse" .)