When Greg Robinson was in charge of the Texas defense in 2004, the Longhorns were physical and productive.They were anything but those things in last weekend’s loss to BYU. The Cougars racked up 550 rushing yards on a hapless Texas defense in a 40-21 win.Defensive coordinator Manny Diaz was fired the next day and replaced by Robinson, who is charged with the task of turning a defense that has allowed the third-most rushing yards in the country into a unit capable of slowing an Ole Miss team whose offense is arguably better than BYU’s.He has his work cut out for him.“It was just unacceptable,” Texas coach Mack Brown said of his team’s performance in Provo, Utah. “You’ve got two choices in life: lie down and point fingers or you can go back to work. They understand when you lose at Texas it’s bad. When you lose like that, it’s really bad.”Brown also said that Diaz anticipated the possibility of him being relieved of his duties and that he made the decision to let Diaz go without consulting anyone. Diaz has since been reassigned to another position within the athletic department. “It’s tough when you lose a coach,” senior defensive end Jackson Jeffcoat said. “As a leader on our defense, I feel responsible for him being gone. It’s not a good thing to feel.” Robinson was the head coach at Syracuse for four years and the defensive coordinator at Michigan two years after that.Before serving as Texas’ co-defensive coordinator with Duane Akina, Robinson spent 10 years as an NFL defensive coordinator, two of them with the Denver Broncos when they won back-to-back Super Bowl titles in 1997 and 1998. The Longhorns went 11-1 and beat Michigan in the Rose Bowl in Robinson’s only year as their co-defensive coordinator, allowing 17.9 points and 107.4 rushing yards per game. This year’s team is giving up 23.5 points and 327 rushing yards per game.“Greg is one of the best teachers out there,” Brown said. “When he was there [in 2004] we were sound fundamentally and we tackled well. It’s tough for him. He had nothing to do with the decision about Manny.”Another concern for Texas is the availability of quarterback David Ash, who suffered injuries to his head and shoulder in the fourth quarter against BYU and is day-to-day. Ash did not practice Sunday.If Ash is unable to play, senior Case McCoy would start at quarterback, with true freshman Tyrone Swoopes being his backup.Also, running back/receiver Daje Johnson injured his ankle against BYU will miss Saturday game against Ole Miss.