"A moment of insanity," Swinney quipped Thursday. "Complete insanity."
Alabama (11-1) slipped into the final spot for the four-team College Football Playoff, despite failing to win its division in the Southeastern Conference.
Alabama was ranked No. 1 until a 26-14 loss at Auburn in its regular-season finale, which handed the SEC West title to the Tigers. Alabama got into the playoff after Auburn lost to Georgia in the SEC championship game, combined with Wisconsin falling to Ohio State for the Big Ten title.
Now, it's Clemson vs. Alabama for the third year in a row in the playoff.
They'll meet New Year's Day in a semifinal at the Sugar Bowl, having met the last two years in the national championship game.
Sitting next to Tide coach Nick Saban during an appearance by all playoff coaches at the College Football Hall of Fame, Swinney blamed his vote on fatigue. He cast his ballot on the bus ride back to Clemson after his team routed Miami for the Atlantic Coast Conference championship.
"Just coming home. Literally, it 3 o'clock in the morning. 'Man, I got to do this poll,'" Swinney recalled, casting a nervous look toward Saban.
The Clemson coach went with the Buckeyes (11-2) at No. 4 behind his own team, Oklahoma and Georgia.
"Looking at it, you know, they won 11 games. Alabama won 11 games," Swinney explained. "They won the Big Ten championship. Obviously, the committee has a lot of things to look at, a lot of data. They're going to pick the four best teams, however they see it.
"At that moment, that's the way I voted. They're all great teams, man."
Saban chimed in at that point, noting that Swinney attended Alabama.
"He was disrespecting his alma mater," Saban said with a smile.
Alabama beat Clemson two years ago for the national title. The Tigers won it all a year ago, edging the Tide on a touchdown pass with a second remaining.
"I'm trying to get rid of him," Swinney said, glancing over at Saban, "but I can't shake him."
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