LOS ANGELES -- He's a 5-foot-8, 165-pound ball hawk who plays with a sharp edge.
Cornerback Nickell Robey is one of the fastest and quickest players on the USC football team. He's stronger than you would think, and he plays with so much leverage that he's able to outfight receivers 7 or 8 inches taller than him for the ball.
But what has made him the most dynamic playmaker on a USC defense that's starting to find its groove doesn't come from his legs, his arms or even his braids-covered head.
"His heart," Trojans coach Lane Kiffin said. "He plays so hard."
It's that vital muscle, though, that has endured so much strain since Robey arrived at USC from his Frostproof, Fla., home two years ago. For Robey, the practice field on USC's campus and the stadiums the Trojans play in are havens from a distant home life that has been in turmoil since he arrived.
Robey's mother, Maxine, died of a massive heart attack just days after he signed his letter of intent to attend USC. It was about then that Robey's father, Earl, lost contact with his son and Robey's younger sister, Maranda. Robey hasn't spoken with his father in nearly two years other than a few occasional words through Facebook. His little sister moved in with an aunt.
"I've just got to move on," Robey said. "I don't think about it too much, because I have a lot to do with school and practice and stuff."
Robey has been a favorite of this coaching staff since Kiffin and his dad, Monte -- then at Tennessee -- started recruiting him during his junior year at Frostproof High. He was good enough to start as a true freshman last season, but it has been in the last handful of games -- starting with the Trojans' Oct. 1 win over Arizona -- that he has shown the playmaking ability to lead this defense from the doldrums.
At times, Robey has been asked to play man-to-man coverage on the other team's best receiver. The defense not only has avoided disaster, but has thrived. Arizona's Juron Criner, a Trojan-killer his entire college career, caught three balls for 29 yards. Notre Dame's Michael Floyd, one of the biggest, strongest receivers in the nation, caught four passes for 28 yards.
Robey has come up with turning-point interceptions in each of the last two games. He picked off Notre Dame's Tommy Rees on the Irish's final drive to preserve a 31-17 victory at South Bend. And Robey found a tendency in Stanford's nearly flawless quarterback, Andrew Luck -- to look the cornerback off and then return to the same receiver -- and stepped in front of a pass, returning the ball 33 yards for a go-ahead USC touchdown with just over three minutes left.
Lane Kiffin thought that was going to be the turning point, not of one game but in this dark spot of USC history.
"Those dark clouds that had started to move Saturday ... there were a lot more of them moving then," Kiffin said.
The Trojans couldn't stop Luck on the ensuing drive and Stanford outlasted USC in three overtimes, but a defense that had been a source of stress for nearly two years now looks like a building block for 2012 and beyond. Much of that sense of optimism comes from Robey's ability to stop the other team's most dangerous threat and to swing momentum in the Trojans' favor.
"Any time you get a guy making plays, it gives the other players on your defense confidence," said USC secondary coach Sammy Knight.
During his 11-year career as a safety in the NFL, Knight played two seasons in Miami with four-time Pro Bowler Sam Madison. When Knight watches Robey, he sees a lot of Madison, who played in the NFL from 1997 to 2008 at 5-foot-11 and 180 pounds.
"A small guy who's tough," Knight said.
When USC's defense was dragging down the program last season and in back-to-back weeks against the Arizona schools this year, it wasn't for lack of athletes. The USC defense is filled with four- and five-star recruits. What it lacked was blue-collar toughness and edge, two qualities that define Robey's game. He also covers 40 yards in 4.3 seconds, making him one of the fastest players on the practice field. Knight said Robey is one of the quickest players he's ever been around.
There's also a joy to the way he plays, a passion that rubs off on teammates. After his touchdown Saturday, he sprinted all the way down the USC sideline, high-fiving fans in the student section.
"I didn't even know if he could go back in," Kiffin said. "He sprinted all the way around the Coliseum, it seemed like. But that's how he practices. That's who he is."
Each day that goes by, Robey, 19, looks more fondly on his decision to uproot and move across the country. During recruiting, his mother had urged him to follow the Kiffins west after they bolted for Los Angeles. Like a lot of Americans, he came to Southern California for a fresh start.
"I feel good when I'm out here, and I feel like it was the best decision for me," Robey said. "To come out here and get away from something that was old and come to something new."
Mark Saxon covers USC football for ESPNLosAngeles.com.