Chargers’ Trevor Williams has turned a big corner as an undrafted free agent out of Penn State

The chip is ingrained on the shoulder of Chargers cornerback Trevor Williams, as much a part of his uniform as the lightning bolt and No. 24 that cover it.

It does not make Williams run faster or jump higher or tackle harder. It does keep an eternal flame lit under the 24-year-old and has been a driving force in Williams going from an undrafted free agent out of Penn State in 2016 to one of the NFL’s top defensive backs in 2017.

“I play with a certain edge — I have an extra chip on my shoulder because I came in undrafted,” Williams said before practice this week in preparation for Sunday’s game against the Denver Broncos. “It’s just something that’s always there, that gives me extra motivation.

“I feel like I have to prove myself every week and to keep making the coaches regret their decision. Every time I step onto the field, for practice or a game, I keep that in mind.”

Jahleel Addae can relate. The Chargers strong safety also reached the NFL as an undrafted free agent, out of Central Michigan in 2013. Four years later, Addae signed a four-year, $22-million contract with the Chargers.

“It’s internal motivation,” Addae said. “Some guys have it, some don’t. Some guys need something like that to get them going, like I did. I know exactly what Trevor has gone through to prove himself and to try to get that ‘undrafted’ tag off him.”

The 5-foot-11, 191-pound Williams, a two-time All-Big-Ten honorable-mention selection, was promoted from the practice squad to the active roster in Week 5 last season. He had 23 tackles, five pass breakups and one fumble recovery in 12 games, five of them starts.

When Pro Bowl cornerback Jason Verrett suffered another season-ending knee injury in the 2017 opener, Williams moved into the starting lineup in Week 2 and has provided what defensive coordinator Gus Bradley called “better than solid play — he’s exceeded expectations.”

Playing 326 of 328 defensive snaps in the last five games, Williams has 22 tackles and five pass breakups. He notched his first career interception in the first quarter of Sunday’s 17-16 win at Oakland, leaping backward to grab an overthrown ball and weaving down the left sideline for a 21-yard return.

Williams also provided tight coverage on receiver Michael Crabtree on a fourth-and-two pass that fell incomplete on the first play of the fourth quarter. The Chargers took over at the 41-yard line and drove 59 yards for a go-ahead touchdown.

Pro Football Focus — an analytics website that rates defenders on coverage, run defense and pass rush — ranks Williams as the 11^th best cornerback in the NFL, with a six-game overall grade of 85.6, which the site considers “high quality.” Chargers Pro Bowl cornerback Casey Hayward ranks 14^th with an 85.4 grade.

“He’s a big corner, and he’s really competitive,” Hayward said of Williams. “I’ve seen the hard work he’s put in, and he’s getting better every week. Teams are taking notice of him.”

Williams has Hayward, in part, to thank. Williams, who grew up in Baltimore, moved into Hayward’s Atlanta-area home for a month last summer. He worked out with him every day and pored over tape with him.

“I wanted to see how he trains, how he takes care of his body, what his daily routine is, what his pregame routine is, everything,” Williams said. “I was pretty much a big sponge.”

Like the paper towels in those old Bounty commercials, Williams was a quicker picker-upper.

“Every play in practice, every rep he gets in a game, you really see him try to stay true to his technique,” Bradley said. “He’s a guy the coaching staff has built a great deal of confidence in. He’s one of those guys where you say, ‘All right, we don’t have to worry about that.’ ”

Bradley believes Williams will continue to excel as long as he relies on his technique, athleticism and instincts, and plays to his strengths.

“Sometimes what can happen with corners is, they do things well, and then they want to start big-play hunting,” Bradley said. “If he stays true to his technique, the plays will come.”

Etc.

Jonathan Smith, a 30-year-old copy machine repairman from Buena Park who was shot in the neck while trying to save dozens of people from a gunman who opened fire on a Las Vegas country music festival on Oct. 1, attended Friday’s practice and met Philip Rivers, Antonio Gates and Melvin Gordon in the locker room afterward. “I feel like a little kid who got his first bicycle,” said Smith, a longtime Chargers fan who will also attend Sunday’s game. “This is something that’s gonna stick with me for the rest of my life.” … Receiver Keenan Allen (shoulder), right tackle Joe Barksdale (turf toe) and defensive lineman Corey Liuget did not practice Friday, and all three are listed as questionable for Sunday’s game. Coach Anthony Lynn said he expects Allen, the team’s leading receiver who was injured when he fell in practice Thursday, to play, but Barksdale and Liuget likely will be game-time decisions. Safety Adrian Phillips remained in concussion protocol but was able to practice Friday. … Defensive lineman Jerry Attaochu, inactive for the first six games, began taking practice reps at outside linebacker this week in an attempt to increase his versatility.

mike.digiovanna@latimes.com

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