The most common and most likely answer to this crossword clue is the 9 letter word RECEIVING
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More clues leading to the result RECEIVING
Buddy explains!

The straight part
We know that "Not serving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not serving = receiving.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 RECEIVING mean?
RECEIVING verb- To take, as something that is offered, given, committed, sent, paid, etc.; to accept; to be given something.
- To take goods knowing them to be stolen.
- To act as a host for guests; to give admittance to; to permit to enter, as into one's house, presence, company, etc.
- To incur (an injury).
- To allow (a custom, tradition, etc.); to give credence or acceptance to.
- To detect a signal from a transmitter.
- To be in a position to take possession, or hit back the ball.
- To accept into the mind; to understand.
- The act by which something is received; reception.