Rosen has not thrown an interception in his last 218 passes, the longest streak in the FBS this season and a new school record. Much of that success comes from improved pass protection and Rosen's understated ability to avoid pressure.
''He keeps plays alive,'' Trojans linebacker Su'a Cravens said. ''He's not necessarily going to scramble or move in the pocket to find a running lane, he's going to do it to keep the play going and find an open receiver and he does it pretty well.''
Rosen has only been sacked 11 times in eight Pac-12 games, the lowest total in the conference this season.
UCLA offensive lineman Caleb Benenoch compared Rosen's overlooked mobility to that of Indianapolis Colts quarterback Andrew Luck. Rosen broke the pocket for a 37-yard touchdown run that put UCLA ahead late in the fourth quarter before losing to Washington State in the final seconds, but usually puts that trait to use in more subtle ways by sidestepping a free rusher or stepping up in the pocket.
''That has been his best quality. He has a lot of tools but that is one thing that makes him so special,'' Benenoch said. ''He is an athletic kid. I think people assume because he is such a great pocket passer that he can't run but he is very athletic and can do that.''
USC struggled against a quarterback capable of extending plays in a similar manner in Oregon's Vernon Adams Jr., who became the first opponent to throw six touchdown passes in a game in school history. Even more frightening, only one of Adams' scoring throws came on a play where he had to move or elude pressure. The rest came with Adams operating from a clean pocket, capitalizing on major gaffes in the USC secondary.
While Adams made his name at Eastern Washington with a frenetic and often wild approach to playing quarterback, Rosen is the prototypical pocket passer and more than capable of turning those same USC mistakes into touchdowns.
Safety Chris Hawkins blamed the defense's issues on uncharacteristic lapses in concentration, allowing touchdown passes of 48, 52, 37, 30, 21 and 26 yards.
''We were just busting coverages. Some people not running up where they were supposed to be, overthinking the plays. Hawkins said. ''Man, I've already moved past last week. It's not even in my mind anymore.''
Defensive lineman Delvon Simmons expects the USC defense to come out with a sharper mindset against UCLA than it showed at Oregon. A win over the Bruins would break a three-game losing streak in the rivalry and send the Trojans to the Pac-12 title game.
''It would be great for me to go out there and get this one, man,'' Simmons said. ''I'm focused on trying to get the win not only for me and my team but so we get the chance to play Stanford and compete for the Pac-12.''
The challenge will be getting to Rosen and bringing him down, which has usually been a key indicator of success under interim coach Clay Helton. USC is averaging 3.75 sacks in its four wins.
''We just got to put pressure on him and collapse the pocket and hopefully he makes a mistake,'' Cravens said.