The most common and most likely answer to this crossword clue is the 6 plus 5 letter word HAMMER THROW
I've seen this crossword clue in The Guardian
H
A
M
M
E
R
T
H
R
O
W
Buddy explains!
The straight part
We know that "event" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case event = hammer throw.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.