Darnold is more a baseball pitcher. We can also see Darnold has a lean to the left that Rosen does not. We want to keep our spine pretty straight during the whole process.
They could both load their back legs a little more, meaning they could start pushing off their back legs with a little more force and knee bend. When it comes to follow-through, Rosen’s back leg is always coming forward. Darnold’s leg is going left before it straightens out. This is all in the hips. Darnold’s hips are locking and they can’t rotate, so the leg kicks out behind. Rosen’s hips are fluid.
Just because I’m more critical of Darnold’s doesn’t mean I don’t think he’s a good quarterback. I think he’s special and worthy of all the praise he’s getting. Darnold doesn’t have horrible mechanics. He’s certainly not Patrick Mahomes when he was at Texas Tech. It’s just that Rosen’s are that nice.
This is another accurate throw off a hitch step. I believe the hitch is part of the whole dropback, rather than him hitching to go to another read. He hitches to throw either what I’m assuming is an off-screen deep route or, if the safety stays over top, to the deep crossing route. He chooses the latter. Great throw.
Rosen has a curl/flat concept to the field side (the side with more grass between the ball and the sideline) and a sort of shallow cross/drive concept on the short side. Pre-snap, he sees the defense is playing one safety deep, and he knows curl/flat beats one-high-safety defenses, so he looks there right away.
He wants to throw to his receiver, but No. 10 gets in the throwing window, so he moves his eyes toward the other linebacker, No. 44. UCLA has a dig route over that linebacker and shallow cross by the running back underneath him. No. 44 shoots up on the running back, allowing Rosen to hit the dig for a first down.