"The first thing you look at is the size, and I truly thought he would be drafted," Beane said. "He was on our draft board, to be drafted. I'm surprised, and you saw his name still sitting there late in the seventh, and you go 'Man, if this kid doesn't get drafted, we're going to have to go after him,' and we did.

"He has a strong arm, and he's got some mobility. I think he's shown improvement during the year and he played in the Senior Bowl. It wasn't too big for him, and I think he's still an ascending player."

The 6-foot-7, 249-pound Jackson was projected as high as a third-round pick and as low as a sixth-round pick, and his size, reach and arm strength helped him as an NFL prospect.

Jackson threw for 3,131 yards and 28 touchdowns on 225 of 407 passing and was intercepted 12 times in 14 games in 2018. Yet his accuracy was an issue in some pre-draft projections. He had a completion rate of 55.8 percent in three seasons at UB.

The NFL's College Advisory Committee also told Jackson that he would not be projected as a first- or a second-round pick in the 2019 NFL Draft.

Jackson spent part of the offseason working with quarterbacks coach Jordan Palmer in California to become NFL ready. Palmer also trained Bills quarterback Josh Allen in preparation for the NFL.