It’s often the death knell for the season when a team has to go to its third quarterback. The reason is obvious: The third quarterback isn’t as good as the starter or the backup. And often, if it reaches that point, the team is in disarray and morale is low. Just look at the Houston Texans, who before the season were considered a likely playoff team. Now, they’re 2-5 and using third-string quarterback Case Keenum after Matt Schaub and Tyler Yates failed miserably. The Minnesota Vikings were a playoff team last season, yet are 1-6 this season after going through Christian Ponder, Matt Cassel and Josh Freeman before going back to Ponder because of Freeman’s concussion. Last season, seven teams used three quarterbacks. Their combined record was 38-74. None made the playoffs. The Pittsburgh Steelers, at 8-8, were the only ones without a losing record. The Arizona Cardinals used four quarterbacks and finished 5-11. So far this season, five teams, including the Eagles, have used three quarterbacks. Their combined record is 12-26. None of those teams has a winning record. The Eagles at 3-5 haven’t reached the level of despair as Houston or Minnesota heading into their game today against the Oakland Raiders. But they also haven’t scored an offensive touchdown in the last two games, as their once prolific offense has ground to a halt. Rookie Matt Barkley, the Eagles’ third quarterback, has played in each of the last two games, relieving Nick Foles two weeks ago when he suffered a concussion and starter Michael Vick last week when he re-injured his hamstring. Foles will start today, but Vick has been ruled out, meaning that Barkley is the backup again. Eagles coach Chip Kelly has cited the “instability at quarterback” for the last two losses. “It’s not all on the quarterback,” Kelly said. “We have to do a better job as a total group. I have confidence in the group. It was the same group for six games that we were on track to set records. It’s not like we’re going to throw the baby out with the bath water and start over again.”