He gives Trojans a feral reserve

USC linebacker Keith Rivers is regarded as a possible first-round pick in the 2008 NFL draft. Fellow linebackers Rey Maualuga and Brian Cushing could be opening-round picks in 2009.

So when USC plays Illinois in the Rose Bowl, the linchpin player in one of college football’s deepest and most talented position groups once again will be on the sideline the first time the Trojans’ defense takes the field.

And that’s just fine with Thomas Williams.

The fifth-year senior from Vacaville, Calif., has made a career of filling spots, playing nearly as much as any starter at all three linebacker positions while remaining a standout on special teams. Teammates this month voted Williams, nicknamed “Hit Man,” the team’s most inspirational player.

“I had a class here a few years ago and the teacher talked a lot about John Wooden’s philosophies and how you had to be prepared to wear a lot of hats,” Williams said. “I didn’t know what that meant when I first heard it. But I do now.”

Coach Pete Carroll described the 6-foot-3, 235-pound Williams as “the best versatility guy we’ve had,” which speaks more to the Trojans’ depth than it does to Williams’ talent.

He started four games this season and finished as the third-leading tackler among linebackers. Williams had 3 1/2 tackles for losses, intercepted a pass and forced two fumbles for a defense that ranks second nationally.

“He’s probably the most valuable player I have in my room,” linebackers coach Ken Norton said. “He’s able to play all three positions as well as the starters.

“I can’t imagine coaching without him. He’s really bailed us out in a lot of situations.”

Williams, who celebrated his 23rd birthday on Christmas Day, struggled through the years to come to terms with his utility status. Now he considers it a blessing.

He acknowledges his good fortune to arrive at USC in 2003, right on the cusp of the Trojans’ surge to six consecutive Pacific 10 Conference titles and six straight appearances in Bowl Championship Series games.

But he also joined a program that became seemingly overloaded with All-American linebackers such as Matt Grootegoed and Lofa Tatupu and NFL draft picks such as Tatupu, Dallas Sartz and Oscar Lua.

After USC won the Associated Press national title in 2003, a trio of super prospects signed on with the Trojans. Rivers arrived in 2004, Maualuga and Cushing a year later.

“I had to understand these kids I’m playing behind are not just Average Joes -- these kids are going to the first round,” Williams said. “These are All-Americans that will be talked about a long time here at USC.”

Williams never envisioned the utility role when he decided to sign with the Trojans out of Vacaville High. Like most top prospects, he had received hundreds of recruiting letters. But the one that came from USC in 2001 stood out.

“I don’t know why that was,” he recalled. “They weren’t the Miami of the times. But I was just so excited.”

Williams experienced culture shock when he arrived in Los Angeles two years later as part of a recruiting class that included running backs Reggie Bush and LenDale White and others.

Vacaville is a city of about 100,000 located between Sacramento and San Francisco.

“Vacaville is not tiny, but everybody pretty much knows each other or knows somebody who knows you,” he said. “Coming here, there’s like nine million people in a very diverse melting pot.”

Williams redshirted in 2003 and played behind Sartz at the strong-side spot -- the tight end side of the opponent’s offense -- in 2004.

He began the 2005 season as a backup but moved into the starting lineup for six games after Sartz suffered a shoulder injury. He also started twice in the middle and learned the weak-side responsibilities as well.

“I’ve got it all down now, but when I first started it was absolutely confusing at times,” Williams said, chuckling at the memory. “Coaches would yell at me and I was like, ‘Man, I have to play three positions! What do you mean I forgot where I’m supposed to be?’ ”

Last season, Williams played as a backup at all three linebacker spots, started twice at fullback -- yes, he played some offense too, though he never carried the ball -- and continued to star on special teams.

This season, he started three games at the strong-side spot and once in the middle.

“He doesn’t get every rep in practice, but it never ceases to amaze me that every game we need him because something happened to one of the guys, he goes in there and plays a whale of a game,” defensive coordinator Nick Holt said.

Williams has been invited to the East-West Shrine Game and is looking forward to parlaying his varied talents into a pro career.

Norton, a former All-Pro and Pro Bowl selection, expects Williams to join his more celebrated teammates in the NFL.

“He’s the kind of guy that will get drafted in the middle to low rounds, but he’ll play for 10 years because he’s smart enough to play on special teams and be a backup,” Norton said.

Williams, though, is focused on the Rose Bowl. The future, he said, begins the next day.

“I’m just real excited to go out there with my friends,” he said. “We’re crossing the finish line as far as our college careers and then it’s time to move on to whatever that may be.”

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gary.klein@latimes.com