With a desire to hit and the ability to grasp things quickly, his teammates in the secondary recognized his enormous potential.
And when Sanu switched to receiver during spring practice, it didn't take long for freshman quarterback Tom Savage to learn his fellow classmate could be an offensive force.
However, after a freshman season in which Sanu displayed his athleticism, maturity and ability by catching 47 passes and rushing for 305 yards, not everything is settled.
Sure, he produced on offense, but could he be an even better safety?
"If I was a coach, and I know you probably can't do it, but I'd play him both ways,'' Rutgers cornerback David Rowe said. "I know that's real rare. He's good enough to do it.''
Sanu didn't exactly balk at the idea.
"It would be fun a situation,'' he said. "It would mean knowing the offensive and defensive game plans. I like playing both. It's fun either way.''
The public got to see Sanu's offensive ability immediately when he opened his career with 10 catches for 101 yards in the season opener against Cincinnati, and his versatility came a few weeks later when he supplanted senior Jabu Lovelace in the "Wildcat'' package.
Although the package operated with moderate success once Sanu took on the duties as the season progressed, his breakout performance came Nov. 27 against Louisville. He ran 18 times for 148 yards.
Sanu is averaging 6.2 yards per carry and has three rushing touchdowns to go with two receiving scores.
"He's a freak of nature,'' Savage said. "Even in the spring game when he caught a pass and dove into the end zone, I knew the kid was special. I was asking, ‘You going to stay at receiver or go back to safety?' He goes, ‘I love hitting.' Nah, just stay a receiver. It's fun.''
His size and physical style of play takes a physical and mental toll on opponents, especially in the secondary.
"The size, the speed,'' Rowe said while shaking his head. "In practice, we'll be tired and he'll just be full go. He'll go until he's tired. That's one thing about Sanu. In the summer, we wear heart rate monitors, and his was out of the roof and he was still going.
"And I don't want to be anywhere near him when he's in the Wildcat. I saw what he did to Louisville, and I don't want to be a victim.''
The public has not seen Sanu play safety.
Fact is, few have.
His time as a safety at Rutgers was limited to a few spring practices. Sanu classifies himself as a "decent'' safety, which doesn't seem too promising, until it is learned he classifies himself as a "decent" receiver as well.
But the player with the highest profile on Rutgers' defense, fifth-year senior cornerback Devin McCourty, is direct when assessing Sanu's defensive ability.
"When I first saw him I was like, ‘Wow, this kid's big,' ‘' McCourty said. "And when I saw him out there hitting people at safety, I said, ‘Wow, this guy's going to play this year and make a few plays,'
"And then they moved him to (wideout), and I was like, ‘Argh, why'd they put him on offense?' ‘'
It didn't take long for Sanu to show why.
The quality of depth in Rutgers' receiving corps has been a source of concern throughout the season. With the secondary established, especially with junior Joe Lefeged at strong safety and senior Zaire Kitchen at free safety, Sanu's best opportunity to garner loads of playing time came at receiver.
Just don't ask Sanu to pick which side of the football field he enjoys more.
"I like safety because I like being physical,'' he said. "I like receiver because I like making plays, and being able to have the ball in my hands.''
Maybe in the future he will be able to do both.