The most common and most likely answer to this crossword clue is the 7 letter word SKITTLE
I've seen this crossword clue in The Guardian
S
K
I
T
T
L
E
More clues leading to the result SKITTLE
Buddy explains!

The straight part
We know that "Knock over/Knock over" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knock over/knock over = skittle.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 SKITTLE mean?
SKITTLE noun- One of the wooden targets used in skittles.
- To play skittles.
- To beat comprehensively.
- To knock down.