The most common and most likely answer to this crossword clue is the 3 letter word PAR
I've seen this crossword clue in The Guardian
P
A
R
More clues leading to the result PAR
Buddy explains!

The straight part
We know that "level" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case level = par.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 PAR mean?
PAR noun- A passage in text that is about a different subject from the preceding text, marked by commencing on a new line, the first line sometimes being indented.
- A mark or note set in the margin to call attention to something in the text, such as a change of subject.
- An offset of 16 bytes in Intel memory architectures.
- Equally distant from one another at all points.
- Having the same overall direction; the comparison is indicated with "to".
- (hyperbolic geometry, said of a pair of lines) Either not intersecting, or coinciding.
- Involving the processing of multiple tasks at the same time.
- A clause, phrase or word which is inserted (usually for explanation or amplification) into a passage which is already grammatically complete, and usually marked off with brackets, commas or dashes.
- Either of a pair of brackets, especially round brackets, ( and ) (used to enclose parenthetical material in a text).
- A digression; the use of such digressions.
- Such brackets as used to clarify expressions by grouping those terms affected by a common operator, or to enclose the components of a vector or the elements of a matrix.
- In the Anglican, Eastern Orthodox, Lutheran and Roman Catholic Church, an administrative part of a diocese that has its own church.
- The community attending that church; the members of the parish.
- An ecclesiastical society, usually not bounded by territorial limits, but composed of those persons who choose to unite under the charge of a particular priest, clergyman, or minister; also, loosely, the territory in which the members of a congregation live.
- A civil subdivision of a British county, often corresponding to an earlier ecclesiastical parish.
- An administrative subdivision in the U.S. state of Louisiana that is equivalent to a county in other U.S. states.
- By; with.
- Equal value; equality of nominal and actual value; the value expressed on the face or in the words of a certificate of value, as a bond or other commercial paper.
- Equality of condition or circumstances.
- (mostly uncountable) The allotted number of strokes to reach the hole.
- A hole in which a player achieves par.
- An amount which is taken as an average or mean.
- To reach the hole in the allotted number of strokes.
- Young salmon, at a stage between fry and smolt when they feed chiefly on invertebrates but cannot tolerate saltwater.
- A young leveret.