It doesn't matter how bad of a Quarterback Kyle Boller is. What matters, for the 4-2 Oakland Raiders, is how much worse Kyle Boller is than Jason Campbell. If Jason Campbell could play well enough at QB (and he wasn't lighting the world on fire with his 3:2 TD-to-interception ratio), surely Kyle Boller could do the same....right? Well, no.
Jason Campbell will never win an MVP Award and will never be a very good QB. He's not accurate enough, he doesn't run well enough to make up for his lack of accuracy, and he throws too many interceptions to go along with too few TDs. Yet, with all of those flaws, he is 11-7 as the Oakland starter and has finished with a QB rating between 84-87 each of the last 3 seasons (in 5.5 games this season, his QB rating is 84.2).
The QB Rating stat isn't a perfect stat. In fact, it does very little to show just how valuable a QB is to his team. What it is a pretty good indicator of is whether or not the QB can play without making mistakes. Philip Rivers didn't make many mistakes before this season, so his QB rating for each of the last 3 years fell between 101-106. This season he's making too many mistakes and he's down to a QB rating of 87.6.
Let's see how Kyle Boller stacks up.
In seasons where he has started at least 4 games, Boller's QB Rating has fallen between 61-76. If you throw out his rookie season and the year he started a few games for the Rams (who were/are really bad), that range shrinks to 70-76.
Kyle's best season came the last time he started for the Ravens, a team that the Raiders try and mimic with their tough defense and strong running game. He started 8 games that year, winning just 2 of them, throwing 9 TDs, 10 interceptions and getting sacked 24 times (sacked on 8% of his pass attempts).
Boller has a strong arm, which was proven when he threw a pass through a goal post at the University of Cal-Berkeley from his knees on the 50-yard line, but his biggest issues as a pro have dealt with not throwing enough TDs. In his only full season as a starter, he threw 11 interceptions (less than what Jason Campbell threw in 2010) but threw for just 13 TDs (compared to 20 for Campbell last year). He is an offense-killer in terms of getting points on the board.
The Raiders passing attack was already a weakness, they're tied for 20th in terms of passing TDs this season, and downgrading from Campbell to Boller could be the straw that breaks and sends the Raiders back out of contention for the AFC West.