It's late in the game and Michigan has a number of backups in. Robert Marve is in at quarterback for Purdue with four wide receivers and a running back in the backfield. Michigan is in their nickel package with Courtney Avery in as the nickelback.
Traditionally in a zone blitz, pressure will come from the linebackers or defensive backs while a defensive lineman drops into zone coverage with the rest of the defenders. It's tough to see here, but I'm relatively certain that Michigan is playing a combination of zone and man principles with the corners and safeties in man coverage against each of Purdue's receivers.
On the snap, Craig Roh begins to drop into coverage. The other three linemen, Kenny Demens, and Courtney Avery all blitz.
The initial rush doesn't create any pressure but Avery and Demens will cause problems in a moment. Brandin Hawthorne is turning to play zone coverage over the middle of the field.
Demens finally gets to the line of scrimmage and Avery is still screaming downfield. Roh is locked onto Marve in the backfield cutting off any passes to the short side of the field.
Not seeing anyone to throw to, Marve steps up into the pocket, but it's quickly collapsing around him.
Avery finally arrives to the play. He and Roh will chase down Marve in the backfield for a sack.
I really like this playcall. It's designed to force a quarterback to one side of the field where there are linemen dropping into coverage. Avery blitzes from the wide side of the field as Roh steps into coverage on the short side. Not only does this force a quaterback to throw into a defense's strength, but forcing the quarterback to the short side of the field gives Roh less field to cover. Hawthorne is also playing zone in the middle of the field and is able to cut off any throws against the grain of the play.
I'm relatively certain this playcall only works against vertical passing routes, but that's exactly what Michigan was facing as Purdue tried to force the ball down the field in garbage time. Short routes or crossing routes would be problematic with this playcall. This blitz is not something we'll see again soon, but any time a team tries to run all/four vertical routes, this is the kind of play Mattison can dial up to attack it.