
This is deeper than most curls plays - mainly because it's 3rd and 10.
NO is running a combo coverage. it's cover 6 with the single receiver side corner playing man. This protects against any rub/pick plays on that side and then allows the corner on the single receiver side to play tight man-man.

At the snap - you can see VD was the primary read on the play(I'm 95% sure). Since CK first locks onto him as the receiver on his mid-in route the safeties take not and play good team defense. The safety on the inside quarter stays in position for an overtop route and the backside safety is ready to drive on any in cutting routes.

As VD comes over the top you see how it creates the horizontall stretch to open up a space. The outside defender has to respect the curl route from the outside receiver since the corner is going to be playing overtop coverage.

From this angle you can easily see CK looking to VD as his primary. He does a very good job of keeping his knees bent and climbing the pocket while keeping his left shoulder forward in a "throwing" position.

You now see how he's moved to Boldin. This is a really good read by CK as he saw how his looking to VD - and the resulting coverage, would open up Boldin. That's a good job of understanding how the concept will work and where his key defender is(the LB)
He then does a good job in his mechanics of driving off his back foot while keeping very nice knee bend. His shoulders are nice a square so he's able to deliver a very accurate pass with a ton of zip.

You see from this angle how the safety was ready to drive on VD's in route so it was very good that CK moved on. He's just finishing his release BTW. Boldin is right in that happy spot between the stretch of the defense.

Boldin makes a nice catch for a first down.