The Northwestern Wildcats were in position to move to 6-0 with a 28-17 lead entering the fourth quarter, but the Penn State Nittany Lions scored 22 unanswered in the fourth quarter to knock the Wildcats from the ranks of the unbeaten.
Rodger Sherman of Northwestern blog Sippin' on Purple puts much of the blame on the defense:
With that football stuff said: you have to do better than that. You have to win that game, up by two scores in the fourth quarter. Instead, Northwestern's defense got absolutely eviscerated in the last quarter. Zach Zwinek got about three or four yards after first contact every carry, and Matt McGloin dinked-and-dunked Northwestern to a fitting death. I don't think he threw the ball downfield more than 10 yards once in the final quarter, but Northwestern couldn't stop it. There was no pressure, and while the coverage was alright, having five guys short, Northwestern couldn't keep all of them from getting the ball.
Sherman also noted that Penn State had a lot of success on fourth down, converting multiple fourth downs during the game.