When Nelson and the Utes ran onto the field, girls bounced in midriff-baring No. 13 Utah jerseys.
Nelson stared across the field until he picked out No. 92 in BYU white, stretching on the other side. Nelson fantasized about going up against Star Lotulelei, who smiled back. The nose tackle loved players with images bigger than their stature. But no reputation could outmuscle Lotulelei.
On the first play of the game, Nelson prepared for a bootleg pass that, if executed, would find DeVonte Christopher on the right edge. Lotulelei heaved and pushed Utah center Tevita Stevens aside. The athletic behemoth drove his helmet into Nelson's torso.
One play into the 94th Holy War, Rice-Eccles Stadium went silent and Twitter went crazy.
"Ow," @RileysAbs said.
As any fan reading this surely seething by now will tell you, Riley Nelson certainly does not play for the Utes (why, the very thought!) and Star Lotulelei would sooner play naked than in a BYU uniform.
But this is not something that merely could have happened. As it has for BYU and Utah players for generations, the two most decorated and discussed players in the game came close earlier in their careers to playing for the enemy.
Before he transferred to BYU, Nelson originally signed with Utah State after choosing the Aggies over Utah on TV in February 2006.
Lotulelei signed with BYU out of high school, but did not qualify academically. He spent two years at Snow College and signed with Utah, where he became an All-American and Morris Trophy winner.
Both rosters are full of players like this, enough that you could almost field an entire team of them.
And it probably wouldn't be too bad.
Onetime Utah recruit Ryker Mathews has proven to be a good blocker for Nelson at BYU. Just imagine if Utes D-lineman Dave Kruger was alongside him on the offensive line, which is where he feared BYU coach Bronco Mendenhall would eventually stick him if he went to school in Provo.
"To be honest," Kruger said. "I can't imagine myself playing at BYU."
But what is a rivalry good for if not imagination?
The butterfly effect is the element of the chaos theory that dictates that any small change has a profound impact elsewhere. Classically, a butterfly flapping its wings may form a hurricane elsewhere in the world.
Nelson going to Utah and Lotulelei going to BYU could have impacted the world beyond recognition. It's possible nothing would be the same as today.
BYU might be in the Big XII, scheduling Michigan and refusing games against Utah as the Utes slogged along in the dying Mountain West Conference.
But if you allow yourself to imagine that little else changed and Nelson signed on with Kyle Whittingham and Lotulelei had gone to BYU, it's easy to come up with a theory that would have them staring each other in the eyes on Saturday.
Nelson would have redshirted in 2006 instead of playing, as he did at Utah State. He would have served his LDS Church mission and returned in 2009 as the change-up quarterback behind Terrance Cain and Jordan Wynn.
When Wynn got injured in 2010 it would have been Nelson, not Cain, who stepped in. Last year, Nelson would have replaced the reinjured Wynn for the final nine games.
Jon Hays would have never come to Utah.
Nelson would have run onto the field to cheers in Logan last week when Wynn was injured because, although Ute fans hate him now, he would have been just as much of a cult-like figure in red as he is in blue.
Perhaps he would have led Utah to a comeback victory against the Aggies as he did for the Cougars a year ago in Provo.
Nelson said he wonders sometimes what would have happened had he gone to Utah.
"You know what?" he said this week. "I have thought about it. I wouldn't get guff for growing my hair long if I was up there."
At BYU, Lotulelei would have been the nose tackle in a 3-4 defensive front and had to fight through even more double teams.
If Lotulelei had put more weight into the wishes of his family, who lived for years in Orem, he would have stuck with BYU after leaving Snow College.
"My dad would take me and my little brother [BYU and Utah recruit Lowell] to the games all the time," Lotulelei said. "The biggest part of that decision was pretty much my parents, my dad wanting me to go over there."
He said this week he could have had just as much success with the Cougars as he had with the Utes.
"They have produced some pretty good defensive linemen out of there," he said.
After recording the sack, Lotulelei sat on the turf next to Nelson, who slowly rolled over, clutching his gut. Satisfied for the moment, the best player in BYU history looked around a silent Rice-Eccles Stadium.
And then, from the southwest corner where the Cougars fans sat, he heard them cheering.
Tribune reporter Jay Drew contributed to this story.
BYU at Utah
P Saturday, 8 p.m.
TV • ESPN2
Coulda, woulda, shoulda?
Utah and BYU's roster are populated by players who chose one school over the other. A few of the most notable:
Could've been Utes
QB Riley Nelson
OL Ryker Mathews
DB Joe Sampson
OL Braden Hansen
Could've been Cougars
DL Star Lotulelei
DL Dave Kruger
RB Harvey Langi (serving mission)
LB/DL Trevor Reilly