BYU quarterback Taysom Hill, a Heisman Trophy hopeful, broke his left leg late in the first half and is likely done for the season. Without him, the Cougars (4-1) never recovered from a 14-point halftime deficit on a night when former star quarterback Jim McMahon had his No. 9 jersey retired.
Garretson, a sophomore who took over for injured Chuckie Keeton in the second half of a Week 3 win over Wake Forest, also ran for a score. He completed 14 of 17 passes for 257 yards and three TDs in the first half, propelling Utah State to a 28-14 lead.
Hunter Sharp had five catches for 173 yards and a touchdown for the Aggies, who were 20-point underdogs. Devonte Robinson had six catches for 98 yards and two TDs.
