See a mark on a billiard ball (4)

I believe the answer is:

spot

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'see' is the definition.
(to spot is to notice or catch sight of)

I don't understand how the rest of the clue works.

(Other definitions for spot that I've seen before include "Observe - place" , "Detect" , "make out" , "Notice - stain - pick out" , "Blob" .)

I've seen this clue in the Evening Standard.

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