Without preparation, extreme nuts tackle river
I believe the answer is:
extempore
'without preparation' is the definition.
(I've seen this before)
'extreme nuts tackle river' is the wordplay.
I cannot quite understand how this works, but
'river' could be 'po' (Italian river) and 'po' is located in the answer.
an anagram of 'extreme' is 'extemre' which is located in the left over letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for extempore that I've seen before include "on the spot" , "unprepared" , "without warning" , "Spoken off the cuff" , "Not prepared" .)