I don't. The critical defensive series in the 4th quarter of the Boise State game was the drive where the D allowed Boise to go 71 yds, burn clock, and get a 2 score lead with ~4 minutes to go.

• USF scored a TD on every 2nd half possession. The fact that they only got one TD in the 4th quarter has everything to do with a BYU offense that finally came alive and burned clock and nothing to do with defensive proficiency.
• Against Arizona, when a defensive stop would have sealed the victory, BYU instead allowed Arizona to drive 65 yds and kick a field goal to make it a one-score game.
• BYU's second-half D was very solid against Utah State. If defensive performances against the Aggies, playing with an injured QB and an all-new coaching staff, are the measuring stick for success, let's all go ahead and give ourselves a pat on the back.
• Utah scored a FG and a TD to pull within 6 late in the 4th quarter. Everyone in that stadium was tense and thought that BYU was melting under pressure again until the offense answered to swing momentum and win the game (do you remember the collective sigh of relief when Jaren ran up the sideline to put BYU within FG range?). BYU forced a turnover on downs with 2 minutes left on the ensuing Utah possession, but the Utes were down 2 scores - the game was already effectively out of reach thanks to the offense.
• Credit where it's due; BYU's defense secured a key, late-game fumble that was critical in the win vs ASU.