The most common and most likely answer to this crossword clue is the 13 letter word DEMONSTRATION
I've seen this crossword clue in The Times
D
E
M
O
N
S
T
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I
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N
More clues leading to the result DEMONSTRATION
- March day in Dorset ain't bad
- Baddy on street serving protest
- March exhibition
- Familiar bit of research in office presentation
- Unexpectedly, Tom ends fixed allowance, causing protest
- Upset, stand it no more — protest!
- Sinner and saint helping at protest
- Fiend runs into position for protest
- Protest fiend with resistance occupying Waterloo maybe
- Manifestation of devils pulling chicken heart out
Buddy explains!

The straight part
We know that "presentation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case presentation = demonstration.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 DEMONSTRATION mean?
DEMONSTRATION noun- The act of demonstrating; showing or explaining something.
- An event at which something will be demonstrated.
- Expression of one's feelings by outward signs.
- A public display of group opinion, such as a protest march.
- A show of military force.
- A mathematical proof.