"I think he was a sophomore," he said. "And just some of the things he was doing were electrifying."
As for now, Williams said: "I don't know if he's scratched the surface yet."
What the 5-foot-10 and 203-pound Byrd lacks in size and breakout speed, he makes up for with instinct. He identifies the play and has an efficiency of movement.
"I've told him, 'You've got the best feet. You come out of breaks and it's no wasted steps,'" Bills veteran linebacker Bryan Scott said. "It's bam! Gone. I'm telling you he is, to me, the best safety in the league."
Byrd credits his father and Williams for helping him get this far — both physically and mentally.
It's one thing to have the advantage of growing up in the shadow of NFL players and coaches. Byrd also understood it was his responsibility to do something with that edge, knowing there were those wondering whether he was getting preferential treatment because of his name.
"There was always that motivation that in some ways you've got to be better than the rest because of where you come from," Byrd said. "And also, I'm a competitor. So anything your dad does, you always want to try to compete with him."
Byrd's already ahead of the pace his father established in setting the San Diego career record with 42 interceptions. Jairus currently has 17, six more than his father had after four seasons.
Gill Byrd, a Chicago Bears defensive assistant, wouldn't be upset if his son passes him.
"I know that drives him to be the one in the family to have the most interceptions in the NFL," he said. "And I love it. He has a singular focus to be the best."
That includes Byrd's approach off the field. Jairus and Gill have established a program called the Legacy Experience, to help fathers and sons build closer relationships.
"To me, that is the one thing that as a dad I'm most proud of," Byrd said. "I think he understands that where much is given, much is required. And he wants to give back to people."
Dad had plenty more to crow about after Thursday. He was alone at the Bears headquarters watching the Bills game, when he saw his son's interception.
"I was jumping around like a little school kid in the office here," Byrd said. "I was just, 'Wow!'"
The Byrds have a reputation for not getting overemotional, so Jairus was a little surprised to hear about his father's reaction.
"That doesn't sound like him, jumping around," Byrd said, breaking into a smile, realizing he did his father proud. "But that's cool.
"That's a dad for you."
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