"The referee of the match."
Translation:Ο διαιτητής του αγώνα.
Sometimes Duolingo plops a sentence from a different skill in while doing repetitions :)
Keeps things interesting, I suppose.
Some words don't change their ending when its "of the" is there any rules
Just about all nouns change their endings in the genitive case -- the only counter-examples I can think of are foreign loan-words that don't change their ending at all, e.g. το παλτό.
Otherwise, in general:
- Masculine nouns in -ος become -ου
- Masculine nouns in -ας or -ης drop the final sigma and become -α, -η
- Feminine nouns in -α, -η add a sigma and become -ας, -ης
- Neuter nouns in -ο become -ου
- Neuter nouns in -ι become -ιου
- Neuter nouns in -μα become -ματος
So also here: ο αγώνας becomes του αγώνα.