The most common and most likely answer to this crossword clue is the 8 letter word SPITBALL
I've seen this crossword clue in The Guardian
S
P
I
T
B
A
L
L
Buddy explains!
The straight part
We know that "what a naughty child might throw" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what a naughty child might throw = spitball.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 SPITBALL mean?
SPITBALL noun- A pitch of a baseball that has been partly covered with saliva, illegal at most levels.
- A balled-up piece of paper, moistened with saliva (by chewing) and shot through a drinking straw.
- To moisten the ball with saliva before pitching it.
- To brainstorm ideas.