Keeton was on the run and looking to gain some extra yards when was tripped up by Kyle Van Noy before being taken down by two other BYU defenders. During his take down that left knee buckled when Keeton was taken to the ground, and resulted in the injury.
Here is what it looked like when Keeton was injured, via Eye On College Football:
The injury will likely cost Keeton his junior season if it is confirmed that the injury is a MCL and ACL tear, and maybe even his 2014 season which could be used as a redshirt year.
In Keeton's place on Friday night was Craig Harrison who 18 of 41 for 185 yards and a touchdown, plus another 38 on the year. Goals and expectations have drastically changed for the 2013 season with Keeton out for an extended period of time.