Learn Russian: Что за издевательство этот глупый перформанс! - What a mockery this stupid performance is!

When за is a normal preposition (meaning "behind" or "for"), it takes the accusative or instrumental case. But here, что за acts together as a fixed, invariable exclamatory particle meaning "What a...!" or "What kind of...?". Because it's acting as a particle and not a true preposition, the noun that follows it stays in the Nominative case.

Why use the English loanword перформанс here instead of standard Russian words for "performance" like спектакль or представление?

Перформанс specifically refers to modern "performance art"—the avant-garde kind you might see in a contemporary art gallery, which can sometimes be bizarre or provocative. Спектакль means a traditional theatrical play, and представление is a show or performance (like a circus act). The speaker is specifically complaining about a weird modern art piece!

How strong of a word is издевательство in this context?

It's a very strong and expressive word. It comes from the verb издеваться, which means to mock, bully, or abuse someone. By calling the performance an издевательство (a mockery or travesty), the speaker is expressing deep indignation—they feel the art piece is practically an insult to the audience.

Could you change the word order and say Что за этот глупый перформанс издевательство!?