Graham Mertz had a disastrous start to his NFL career. In the very first preseason game, he went 7/14 with 27 yards and three interceptions. You may need to read that again: three interceptions in just 14 attempts. That's about as bad as you can get in an NFL preseason game. For many Wisconsin fans, they walked away with a lack of surprise.
The hard part with Mertz is that he wasn't terrible for Wisconsin; rather, he was so overhyped that it was easy to underdeliver. He wasn't great by any stretch, but he was simply blah. He could never live up to the hype and became a bust even at Wisconsin.