At the end of the fourth quarter the Beavs and the Eagles had been going back and forth with neither team actually able to stop the other, there was only one punt in the second half and that was when the backup quarterback for EWU came in. After the Beavs had gotten the lead back with approximately five minutes back, fans were looking for the one stop to deliver the win, though it would never come. There was a third down assisted by an illegal procedure penalty but that was quickly taken care of for a first down. The Eagles continued down the field until they reached the Oregon State four yard line and a goal line battle ensued.
From the four yard line the Eagles tried to slam it into the end zone. Though they might have just been killing the clock, since it looked like the Eagle quarterback might have slid down at the four as opposed to just taking it in. Regardless of that notion, the runs continued to eat up the clock forcing the Beavs to call their last two timeouts. On third down quarterback Jordan Adams threw to his right where Sean Martin was called for pass interference.
This play was the critical moment of the game. Worst case is that it is a touchdown and the Beavers get the ball back with a minute left, and with what they accomplished in 15 seconds they would have had a genuine shot to get the ball much further down the field. Best case is that it goes incomplete and it would have moved to fourth down with the clock still stopped. Both of those options are far superior to what actually happened.
It's always tough to take one play because of the butterfly effect of how the rest of the game would change. The only real effect would be if they went for a field goal as opposed to a touchdown, but the Eagles already seemed plenty confident of their offense and almost certainly would have gone for it on fourth down.
That penalty essentially took away 40 seconds in the most likely case and made a final comeback almost impossible, and as such it was the critical moment of the game.