This video shows the ref reaching for his flag immediately after the hold, and well before Retzlaff goes down. Even when the flag is thrown, Retzlaff isn’t down yet.

But the Ksl article claims that he was sacked, and then a penalty was called.

The Utah postgame press statement also called it a “late thrown flag.” Noting late about it from what I see.

https://twitter.com/50stev/status/1855542663249904068