Correct spelling, explanation: the word referee comes from the word refer combined with the suffix -ee. This suffix is used to form a noun from the verb describing a person that is an object of the action specified by the verb (for example employee). This suffix does not require doubling the last consonant as it begins with a vowel. That’s why referree is incorrect and the right way to spell this word is referee.

Definition of referee:
noun, a person given the power to arbitrate; often: a judge in a sports game, especially football
The main referee should not only follow the action on the whole field but also support field referees.

Incorrect spelling, explanation: referree is the wrong form since there is no need to double the consonant r with the suffix that starts with a vowel (here: -ee). The correct form, referee, is a combination of the word refer and this suffix, -ee.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling