The most common and most likely answer to this crossword clue is the 13 letter word COMPLEMENTING
C
O
M
P
L
E
M
E
N
T
I
N
G
Buddy explains!

The straight part
We know that "Balancing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case balancing = complementing.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 COMPLEMENTING mean?
COMPLEMENTING verb- To complete, to bring to perfection, to make whole.
- To provide what the partner lacks and lack what the partner provides, thus forming part of a whole.
- To change a voltage, number, color, etc. to its complement.
- Old form of compliment