The most common and most likely answer to this crossword clue is the 9 letter word OUTLAWING
I've seen this crossword clue in The Guardian
O
U
T
L
A
W
I
N
G
Buddy explains!

The straight part
We know that "Banning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case banning = outlawing.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 OUTLAWING mean?
OUTLAWING verb- To declare illegal.
- To place a ban upon.
- To remove from legal jurisdiction or enforcement.
- To deprive of legal force.