The most common and most likely answer to this crossword clue is the 1 plus 5 plus 3 plus 2 plus 5 letter word A TOUGH NUT TO CRACK
I've seen this crossword clue in Financial Times
A
T
O
U
G
H
N
U
T
T
O
C
R
A
C
K
Buddy explains!
The straight part
We know that "Tricky opposition/Brazil" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tricky opposition/brazil = a tough nut to crack.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.