Boulder, Colo. ? The Colorado defense that was supposed to be the backbone of the team is struggling after three games with a trip to No. 10 Florida State looming this weekend.

“It has been a puzzle,” Colorado coach Gary Barnett said Monday. “I guess I misread them. That’s all I can say.”

The defense is allowing 430.3 yards and 32 points per game, 99th and 93rd nationally in those categories. The woeful effort has coaches looking at cornerbacks Phil Jackson and Sammy Joseph in particular.

“Frankly, Phil has to play better,” cornerbacks coach Vance Joseph said. “He’s been a four-year starter, but it’s a business and it’s an every-day business. Every day you’ve got to make a play.”

Colorado (2-1) started the season by beating rival Colorado State and UCLA, but dropped out of the Top 25 after Saturday’s 47-26 blowout loss at home to Washington State. It doesn’t get any easier Saturday against the Seminoles and their athletic passing attack.

The mistakes Colorado defenders got away with early in the season caught up to them last week.

Sammy Joseph whiffed on a tackle that allowed a 74-yard touchdown reception, while another receiver was all alone for a 77-yard score.

“Those things can’t be tolerated on this defense, especially at that position,” Vance Joseph said. “We’re the last line of defense. I need guys who can make those plays. So now it’s tough love.”

Colorado is considering changes on defense, including playing freshman Dominique Brooks at safety. Barnett also said redshirt freshman Thaddaeus Washington could see time at linebacker.

Senior safety Clyde Surrell has completed his legal obligations for violating parole and should add maturity to a defense that at times played four freshmen in its six-back dime package against Washington State.

Asked if he attributed the defensive mistakes to the youth, Surrell replied: “I can’t really blame it on them. It basically comes down to our older guys, the seniors.

“We’ve got to step up. It’s a team loss.”