The most common and most likely answer to this crossword clue is the 5 plus 3 plus 6 letter word SOUTH SEA BUBBLE
I've seen this crossword clue in The Times
S
O
U
T
H
S
E
A
B
U
B
B
L
E
Buddy explains!
The straight part
We know that "Financial crash" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case financial crash = south sea bubble.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.