The most common and most likely answer to this crossword clue is the 9 letter word EQUIPOISE
I've seen this crossword clue in Independent
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The straight part
We know that "Balance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case balance = equipoise.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 EQUIPOISE mean?
EQUIPOISE noun- A state of balance; equilibrium.
- A counterbalance.
- To act or make to act as an equipoise.
- To cause to be or stay in equipoise.