them would have doomed our ability to win the national title. The same case could be made for the last several games of 1996, plus of course the game we lost that year to Washington.
In 1990, when Ty was trying to win the Heisman, the Miami game we won and the Oregon game we lost were both critical, and all the games we played toward the end of the year were too; including one we lost to Hawaii the night Ty won the Heisman, when we were ranked #4 — at that point we still had an chance to play for the national championship, or to at least finish ranked high enough to have a legitimate argument for it.
In 2001, the last few games, including the one we lost to Hawaii in December, were critical to our push to be BCS-busters. Likewise in 2020; the game vs. Coastal Carolina probably kept us out of a NY6 bowl game.
Other massive BYU regular season games through the years include Georgia in 1982, UCLA in 1983, UCLA and Air Force in 1985, Texas A&M in 1996, Wyoming in 1999, TCU in 2006/2008/2009, Oklahoma and Florida State in 2009, various utah games through the years, and I'm sure there are a bunch of others I have left out.