"Denver typically relies on four players to do most of its pass-rushing damage, but it clearly saw the success other teams have had in bringing extra pressure at Smith. When teams don’t blitz, Smith ranks an Alex Smith–like 20th in QBR, right about league average. When teams do blitz, his QBR drops from 62.8 to 25.9 — the fifth-worst mark in football."
http://grantland.com/the-triangle/nf...rs-and-losers/