Vikings coach Brad Childress is defending his decision to keep Tarvaris Jackson as the team's backup to starting quarterback Brett Favre. Minnesota traded Sage Rosenfels to New York on Friday. Rosenfels had better numbers in the preseason, but he mostly worked with the second team. "It's a completely different set of circumstances," Childress said. "I would hope that if Tarvaris was in there going with the twos, that he would have been able to light it up that same way."