The most common and most likely answer to this crossword clue is the 7 letter word BEGORRA
I've seen this crossword clue in Independent
B
E
G
O
R
R
A
Buddy explains!
The straight part
We know that "As a leprechaun might say, I’m surprised" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as a leprechaun might say, i’m surprised = begorra.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.
What does BEGORRA mean?
BEGORRA interjection- An exclamation of surprise.