http://sports.espn.go.com/nfl/notebook?page=sundaycountdown07
Chargers D is much more aggressive
The Chargers' defense has completely changed since playing the Patriots in Week 2. During that game, the Chargers were in a bend-but-don't-break scheme and never pressured Tom Brady nor challenged the Patriots' WRs. Even more surprising, LBs Shawne Merriman and Shaun Phillips were dropping back and playing man-off zone coverages rather than attacking the quarterback. This soft defensive scheme is how the Chargers played up until Week 10.
After being destroyed in Week 9 by the Vikings, San Diego changed its defensive philosophy the next week against the Colts. The Chargers became more aggressive. Merriman and Phillips started attacking off the edges and getting pressure on the quarterback. During this game Peyton Manning threw six interceptions, including three to CB Antonio Cromartie, who took over the starting role. With Cromartie starting, the Chargers had three quality cover corners because CB Drayton Florence became the nickel back. With three good CBs the Chargers have been able to play more tight man-to-man coverage schemes with two safeties in zone over the top. This is very important because it doesn't compromise the team's ability to pass rush.
Since the Chargers' defensive turnaround, they are attacking more, creating a great pass rush, running some creative schemes and using zone blitzes. They are even bringing Merriman and Phillips through the same gap. Overall, the defensive adjustments the Chargers have made make them a better team.