Answer:
An expert on word games
Step-by-step explanation:
Looking at the sentence, we discover that "An expert on word games" are the words that form the appositive phrase.
Appositive phrases refer to words that come before or after a noun or pronoun to identify, modify or explain it.
Sometimes, they can be marked off by commas in the middle of a sentence; such are known as nonrestrictive. If the phrase is placed at the end of the sentence, a comma should be used to precede it. Also, if it begins a sentence, comma should be used to set it off in the sentence.