The most common and most likely answer to this crossword clue is the 11 letter word PEACEKEEPER
I've seen this crossword clue in Independent
P
E
A
C
E
K
E
E
P
E
R
More clues leading to the result PEACEKEEPER
Buddy explains!
The straight part
We know that "one tries to prevent a shot?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one tries to prevent a shot? = peacekeeper.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.