The most common and most likely answer to this crossword clue is the 12 letter word ECCENTRICITY
I've seen this crossword clue in The Daily Telegraph
E
C
C
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Buddy explains!
The straight part
We know that "Strange behavior/that is noticeable in The Oval" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case strange behavior/that is noticeable in the oval = eccentricity.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 ECCENTRICITY mean?
ECCENTRICITY noun- The quality of being eccentric or odd; any eccentric behaviour.
- The ratio, constant for any particular conic section, of the distance of a point from the focus to its distance from the directrix.
- The eccentricity of the conic section (usually an ellipse) defined by the orbit of a given object around a reference object (such as that of a planet around the sun).