Hurting Carson Palmer's chances of outperforming historical averages are his injures. Kimo von Oelhoffen did a number on his knee in 2005. Ligament tears are relatively standard, but damage to cartilage and meniscus is far more serious and Palmer suffered both. That said, Palmer was never a scrambler, has not suffered any kind of spike in sack percentage (Palmer has consistently outperformed league average (and sack percentage is the most consistent stat when a quarterback changes teams)), and has not missed additional time because of the injury. As much as it's possible, the knee injury is a thing of the past.
Palmer missed 12 games in 2008 because of a partially torn tendon and ligament in this throwing arm. That ended a streak of 51 games started. He has since started 33 straight games. Hasselbeck's career long is 35, and that ended in 2004. Palmer elected to rest and rehab instead of undergoing Tommy John surgery, which seems ill-advised, and may contribute to his below average completion percentage and interception percentage. It's something to consider at the very least.
And if we're considering injury-related decline, we should probably talk about his declining performance passing the ball deep:
2005
| Distance | Comp/Att | Yards | TDs | INTs |
| 21-30 | 11/25 | 271 | 5 | 0 |
| 31-40 | 9/19 | 383 | 5 | 3 |
| 41+ | 3/12 | 165 | 1 | 0 |
2006
| Distance |
Compl/Att | Yards |
TDs |
INTs |
| 21-30 |
12/35 |
384 |
3 |
0 |
| 31-40 |
9/24 |
424 |
4 |
1 |
| 41+ |
4/12 |
205 |
2 |
1 |
2007
| Distance |
Comp/Att |
Yards |
TDs |
INTs |
| 21-30 |
13/36 |
323 |
4 |
3 |
| 31-40 |
2/18 |
73 |
1 |
2 |
| 41+ |
6/14 |
286 |
3 |
1 |
2008
| Distance |
Comp/Att |
Yards |
TDs |
INTs |
| 21-30 |
2/6 |
42 |
1 |
1 |
| 31-40 |
0/3 |
0 |
0 |
0 |
| 41+ |
0 |
0 |
0 |
0 |
2009
| Distance |
Comp/Att |
Yards |
TDs |
INTs |
| 21-30 |
3/15 |
146 |
0 |
1 |
| 31-40 |
1/9 |
40 |
0 |
2 |
| 41+ |
3/10 |
135 |
0 |
2 |
2010
| Distance |
Comp/Att |
Yards |
TDs |
INTs |
| 21-30 |
7/22 |
224 |
2 |
2 |
| 31-40 |
5/13 |
251 |
4 |
1 |
| 41+ |
2/11 |
99 |
0 |
1 |
Now, other things are at play here. The Bengals line was pretty good in 2005. It started a still promising Levi Jones at left tackle, and sub-elite left guard Eric Steinbach. Steinbach signed with Cleveland in 2007. Jones, however, missed most of 2006. Then-rookie Andrew Whitworth took over, and has since settled in as the Bengals starting left tackle the last two seasons. Whitworth is a suspect pass blocker, and the Bengals attempted to replace him by drafting Andre Smith. All-Pro right tackle Willie Anderson was at his peak from 2004-2006. He missed significant time in 2007, was cut, signed with the Ravens and has since retired. Rudi Johnson was at his peak. That was when Johnson was a high-volume power back that demanded safety attention. So, protection, a run game, Palmer had the two elements so often cited as a quarterback's best friend.
How much of Palmer's decline can be attributed to his surrounding talent is impossible to say, but that decline is too often overstated. By DYAR, Palmer's 2010 would rank as Hasselbeck's second best season ever, only behind Matt's amazing 2005. And, in fact, by DYAR, which accounts for playing in a division that includes the Ravens and Steelers, Palmer has been a superstud.
2004: 430 DYAR (17th ranked among qualifiers); 3.9% DVOA (16)
2005: 1,509 (2); 32.5% (3)
2006: 1,189 (3); 21.7% (4)
2007: 1,215 (6); 20.1% (9)
2008: 54 (30); 5.0% (29)
2009: 739 (15); 12.9% (18)
2010: 1,003 (10); 13.6% (17)
For those unfamiliar with DVOA and DYAR, think of it like quarterback rating but opponent adjusted, including sacks and not moronic. Palmer does not perform quite as well by other standards. His adjusted net yards per attempt is just below league average. His EP/A is just above. Neither accounts for opponent adjustment though, and that can not be ignored. Baltimore and Pittsburgh are consistently two of the best defenses in the NFL.