The list of reasons why it's a bad idea to tweet is lengthy, but Notre Dame coach Brian Kelly found a new one last season when, with his defensive coordinator under fire from fans, Kelly's account "liked" a suggestion that Kelly fire the assistant.
Despite Kelly's explanation that the "like" was an inadvertent mistake by a staffer, the digital mishap cemented the impression that the season and maybe the program were slipping out of Kelly's control.
That might have been the lasting image of Notre Dame's 2016 campaign … were it not for a game a few weeks later.
Hurricane Matthew lashed Notre Dame's game at North Carolina State, yet amid the heavy winds and rain Kelly called for 26 passes. The Fighting Irish passed for just 54 yards. It lost 10-3. Its center, snapping the ball, looked like a man trying to corral an eel with his bare hands.
Afterward, Kelly complained that the player was "atrocious" — never mind that Notre Dame insisted on sticking with the shotgun formation.
Observers wondered if this was the death knell of Kelly's time at Notre Dame. His defense was fatally leaky. His offense passed to a fault.
A year later, as No. 11 USC prepares to play No. 13 Notre Dame, some of the same pundits are wondering whether Notre Dame is a dark-horse playoff contender. Saturday's game could be the rivalry's most significant since 2006, when USC was ranked No. 3 and Notre Dame was ranked No. 6. It will be the first time the rivals have met when each has had one loss or fewer since 2009.
USC will see a Notre Dame hat barely resembles last season's team. Kelly and Notre Dame forged a turnaround by rededicating themselves to an aggressive defense and a run-first offense.
Notre Dame has defeated lesser opponents handily. It easily dispatched No. 18 Michigan State. Its one loss was to Georgia, the nation's third-ranked team, by one point.
"I knew that we were in a different place with our football," Kelly told reporters of that game. "I felt good about my football team."
USC coach Clay Helton said he has noticed a “change of philosophy” in Kelly’s offense: “They truly believe in running the ball first to set up the pass game.”
Notre Dame attempts eight more rushes per game this season. Its average has ballooned from 4.5 yards per rush to 6.9, third-best in the nation.
Running back Josh Adams already has 776 yards rushing — more than even Heisman Trophy front-runner Saquon Barkley of Penn State. Adams averages 9.0 yards per carry.
Notre Dame’s reversal on defense has been just as dramatic. It turned out that last season’s infamous tweet, sent by someone whose photo is a person in a gingerbread man costume, had some merit. Kelly did fire defensive coordinator Brian VanGorder, in the middle of the season.
VanGorder’s replacement, Mike Elko, brought an attacking style that has created game-changing turnovers. Notre Dame is 17th in the nation with 14 turnovers forced. It has converted 11 into points.
USC has lost 16 turnovers but has allowed scores after just four of them.
The game is crucial for both teams. "We're pleased with where we are at the halfway point, but this is not where we want to be as a destination," Kelly said.
Notre Dame is very much alive for the College Football Playoff but plays four ranked teams in its final six games.
USC has limped through several games but has an easier second-half schedule. Notre Dame is the best team remaining. A win would set up USC well for the Pac-12 championship game with a shot at the playoff.
"I think we've got two good ball clubs right now, I'll be honest with you,” Helton said. “There are a lot of high stakes on the line."
USC's game at Arizona State on Oct. 28 was scheduled for 7:45 p.m. and will air on ESPN. … For the first time this season, Las Vegas lists USC as the underdog in Saturday's game at Notre Dame.
Follow Zach Helfand on Twitter @zhelfand