In high school, Tim Boyle threw an INT once every 24 attempts. At UConn he threw an INT every 21 attempts. At Eastern Kentucky he threw an INT every 15 attempts. And in the NFL he’s thrown an INT every 13 attempts.
Tim Boyle has a 7.5% INT rate in the NFL. (League average is around 2.3%.) And he had a 4.7% INT rate in college.
How does someone like this make it to the NFL, much less as the preferred backup that is now starting?
I’ve heard stories from the Patriots draft room about Bill ignoring scouts and drafting who college buddies tell him to. He probably had a coach with ties to the NFL and was able to get in that way. If you buddy up with the starting QB or with the coaches, you will be in the league for a while. If you have enough connections, you can make it to the league. He probably also did some things in camp, which made it easier to keep him.