The most common and most likely answer to this crossword clue is the 9 letter word OBSERVING
I've seen this crossword clue in The Guardian
O
B
S
E
R
V
I
N
G
More clues leading to the result OBSERVING
Buddy explains!

The straight part
We know that "Watching" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case watching = observing.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 OBSERVING mean?
OBSERVING verb- To notice or view, especially carefully or with attention to detail.
- To follow or obey the custom, practice, or rules (especially of a religion).
- To take note of and celebrate (a holiday or similar occurrence).
- To comment on something; to make an observation.
- Observation