https://books.google.com/ngrams/graph?content=from+left+field%2C+out+of+left+field&year_start=1800&year_end=2019&corpus=26&smoothing=3&direct_url=t1%3B%2Cfrom%20left%20field%3B%2Cc0%3B.t1%3B%2Cout%20of%20left%20field%3B%2Cc0

I would translate this as на ровном месте.

"from left field" sounds as an excuse, it's understandable that one is not prepared
"на ровном месте" - an aggravating factor, there is no excuse for a failure, or one deserves extra credit if "ровное место" is viewd as a hindrance

*LIKE an excuse. I didn’t understand any of that. Sorry.