It’s a lesson as tempers flare

Like each of the 10 tailbacks vying for playing time in USC’s overcrowded backfield, Stafon Johnson longs for spotlight opportunities.

The sophomore got two for different reasons Wednesday during a spirited and aggressive workout that marked the Trojans’ first practice in shoulder pads.

Johnson, the former Dorsey High star, took a handoff and ran over cornerback Vincent Joseph, drawing cheers from teammates and observers along the sideline. However, as the play continued, safety Will Harris wrapped up Johnson and added a few choice words as well, inciting Johnson to throw the ball at the defender.

Coach Pete Carroll immediately got into the running back’s face, then halted practice for an expletive-laced speech to the team about avoiding unsportsmanlike-conduct penalties.

“It’s so important and such a great issue for the young guys, I had to stop it right there,” Carroll said. “It’s just one of those times you’ve just got to make a statement. I wanted to put my arm around [Johnson], like ‘thanks for the opportunity.’

“He was perfect about it. It wasn’t about him at all. It was the issue.”

Said Johnson of throwing the ball: “It was just the heat of the moment. . . . Coach was just trying to teach me to keep to myself and play ball.”

Johnson responded with several more impressive carries, including a long touchdown run at the end of practice.

It is the kind of play Johnson hopes to repeat in games this season after carrying the ball only three times for 17 yards in 2006, a resume that fueled speculation he might transfer.

Johnson, however, is in the thick of the competition for playing time, according to running backs coach Todd McNair.

“He’s turned the corner mentally,” McNair said. “He’s grown within the program and. . . he’s making good plays and rolling.”

Harris, a third-year sophomore from Covina, appears intent on making up quickly for two seasons lost to injury.

Along with inciting Johnson, he leveled freshman running back Joe McKnight and intercepted a pass. Harris acknowledged he enjoys verbal gamesmanship as much as contact.

“There’s been two years of buildup and it had to come out sometime soon,” he said, smiling.

Carroll will miss practice today to attend the funeral for former San Francisco 49ers coach Bill Walsh, who worked as a team consultant when Carroll was on the 49ers’ staff in the mid-1990s.

“He was extraordinarily open and giving and willing to help and teach,” Carroll said.

Freshmen running backs Marc Tyler and Broderick Green and freshman receiver Brandon Carswell practiced for the first time after receiving varying degrees of certification from the NCAA Clearinghouse. Tyler received full certification. Green and Carswell are allowed to practice during a 14-day review period, according to Carroll, who had called the NCAA on Tuesday. . . . Sophomore Alex Parsons, who played defensive tackle last season, switched to the offensive line and worked at left tackle. . . . Linebacker Luthur Brown sat out most of practice after straining a hamstring, Carroll said.

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gary.klein@latimes.com