The most common and most likely answer to this crossword clue is the 7 letter word ARBITER
I've seen this crossword clue in The Times
A
R
B
I
T
E
R
More clues leading to the result ARBITER
- Judge rarebit cooked
- Judge prepared rarebit
- Judge a Republican, one using his teeth
- Referee, endlessly hard, one using teeth
- Umpire given a mouthful between runs?
- . Judge‘s rare outburst interrupted by boring part
- Judge alligator’s skin by similarly carnivorous animal?
- Judge gets a rare snack next to river
- Judge observing a right tooth, say?
- Judge‘s a right attack dog, perhaps
Buddy explains!

The straight part
We know that "Umpire" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case umpire = arbiter.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 ARBITER mean?
ARBITER noun- A person appointed, or chosen, by parties to determine a controversy between them; an arbitrator.
- (with of) A person or object having the power of judging and determining, or ordaining, without control; one whose power of deciding and governing is not limited.
- A component in circuitry that allocates scarce resources.
- To act as arbiter.