Flynn gave a commitment to David Cutcliffe and Duke back on June 6. But at the 11th hour, after losing Grant Perry to Jim Harbaugh and Michigan, Northwestern and Pat Fitzgerald called up Nagel and made him an offer. It was one he couldn't refuse. Nagel is a local product--the fourth player from Illinois in Northwestern's class--and was named the Chicago area offensive player of the year by Chicago Football in December.
Nagel also has a connection to Northwestern. His older brothers, Aaron and Brett Nagel, both played at and graduated from Northwestern (Aaron was a transfer from Notre Dame). So when the offer came from Fitzgerald, Nagel deliberated, and eventually chose to flip his commitment.
So who is Flynn Nagel on the football field? He's a well-built, compact slot receiver who isn't long or freakishly athletic, but is quick and crafty, and is a good route-runner. He doesn't have elite straight-line speed, but makes up for it with his feel for the position. He will apparently be trained by Jeremy Ebert over the offseason, if you want to take anything away from that. So essentially, he's that guy who'll never draw double-coverage, but who'll be a pain in an opposing defense's rear end.
Nagel isn't a like-for-like replacement for Grant Perry in the class, but he's certainly a type of player Northwestern could use. This was a great get for Pat Fitzgerald in crunch time. The 2015 recruiting class has two big receivers (Cameron Green and Charlie Fessler) and a tiny one (Jelani Roberts), but didn't have that inside possession receiver like Nagel.
It's reasonable to consider the possibility that Nagel could see the field very early in his career. He seems to be mature from a football sense, and although Fitzgerald apparently didn't rate him as highly as Roberts and the others, most recruiting sites like him as a prospect. Northwestern is thin at receiver too. So while we always caution against expecting too much from guys early in their career, don't sleep on Nagel.