I had a hard time sorting out the BYU-Memphis brawl, until I played it backward. Here is what I saw:

Nacua sucker punched #40, apparently splitting his forehead open.
BYU coaches dragged a bunch of their own players into the fray.
Nacua was laying down and got up, right into a random fist.
Nacua then got mad, swung wildly and ran back to the sideline.
Koroma was on the ground when some BYU players dragged some Memphis players on top of him.
One of the Memphis players stepped on his crotch and he popped up quick.
Koroma started fighting the three guys.
One Memphis player kept holding his helmet up to Koromo's head and pulling it away quickly.
Most the other Memphis players got bored and left the fight.
It was one on one until Koroma turned his back on the last Memphis player, who then shoved his head.
Koroma spun around and shoved the player back.
And then, inexplicitably, Koroma lunged backward, striking the outstretched arm of some passing Memphis player.

Wild fight. The game was stranger. After Memphis got a game tying PAT, Bronco had to take two timeouts to calm himself down.
Spoiler Alert: it ended in a scoreless tie.