Following up: Getting after the quarterback

The San Francisco 49ers' Aldon Smith and the St. Louis Rams' James Hall scored two-point plays last season with sacks resulting in safeties.

The sacks these and other players collected outside the end zone affected point totals in less direct ways. As Brian Burke explained in 2008, one sack could represent a two-point change in expected scoring (the difference was 1.7 points without resulting fumbles).

A sack's value changed relative to field position and down-and-distance.

"Knowing that a first-and-10 in another first down 67 percent of the time, a sack that forces a 2nd-and-15 changes the chance to 38 percent," Burke wrote. "A sack on second-and-5 that forces a third-and-10 changes the chance of a first down from 75 percent to 35 percent. Generally, a sack drops an offense's chances of converting a first down by roughly 30 percentage points."

Which helps to explain why the NFL values pass-rushers so highly.

The chart below reflects a continuation of the item that Seattle Seahawks defensive coordinator Gus Bradley inspired Monday. Bradley said he's hoping Seattle can improve its sack totals on early downs in particular.

First-down sacks were particularly scarce for Seattle and St. Louis. Those teams had eight apiece, which ranked tied for 25th in the NFL last season. Arizona led the league with 18 first-down sacks. The Cardinals' Sam Acho had four of his seven sacks on first down.

Bradley told 710ESPN Seattle that his team might have an easier time unleashing additional blitz packages on early downs this season, in part because there's additional preparation time this offseason.

2011 NFC West Sacks by Down (min. 3)