A famous frog once sang, "It's not that easy bein' green."

Stephfon Green could have gone the Kermit route and sung a similar tune last year.

But rather than sulk during a redshirt freshman season, the Penn State running back worked his tail off and is now threatening to leapfrog into the No. 1 tailback slot.

Still, the swift Green must prove he's equipped to shoulder the workload despite his slight stature and the fact that he's green, so to speak.

According to the 5-foot-10, 195-pound Green, he's never logged more than 12 carries in a game, aside from pee-wee football. It's not like the Bronx native couldn't handle the load. But a high school knee injury cut short his senior season and before that he only played one half of games for mighty John F. Kennedy.

"I don't like to be cocky, but I was out by halftime," Green said. "Before I got hurt I had 50 carries for 740 yards. I averaged 14.8 yards a carry. One game I carried it six times and I was out of the game. I had 133 yards."

Because of his limited exposure, Green was relatively unheralded as a recruit. In fact, because of his superior speed he was projected as a cornerback instead of a workhorse running back. But the Nittany Lions coaches quickly learned that Green could be a valuable weapon on offense and word leaked last season that this freshman was dusting the first-team defense.

"The thing that Stephfon gives us is the home-run threat," offensive coordinator Galen Hall said, "which we haven't had since I've been here."

The problem, if you could call it that, was that the Lions already had themselves a budding young tailback. Evan Royster had, by all accounts, a breakout freshman season. Plus, he's a between-the-tackles type of runner, which Penn State traditionally favors. If Green had any chance of getting on the field, it was assumed his size would limit him as a change-of-pace tailback.

"My heart makes up for my weight and my height," Green said. "I feel like I can carry the ball 25 times a game. I don't like when people say I'm just a third-down or situational back. That's an insult, because I feel like I work hard every day on and off the field."

The "insult" wasn't coming from the coaching staff. Whether Joe Paterno was trying to motivate Roysters, the coach officially opened the competition earlier this month when he was asked about Green's durability.

"I think he can handle 20, 25 [carries]," Paterno said. "He's a little bigger kid than you think. He's not tall, but I think he came into camp about 190, 192 pounds. He's a good, solid kid. He's in great shape."

Green, widely considered the fastest on the team, has said he's been clocked at 4.25 seconds in the 40-yard dash. Despite the added weight - he came to Penn State at around 180 pounds last year - Green insists he's maintained his legs.

"I haven't lost a step," Green said. "I'm trying to get up to 200 [pounds], but let's keep that on the low because the coaches don't want me at 200."

Penn State fans got their first glimpse of the motor in the Blue-White game when Green, on his first carry, rocketed through the left side of the line and raced down the sideline untouched for a 57-yard touchdown. He was the game's leading rusher with 87 yards on, go figure, 12 carries.

Royster, all of sudden it seemed, became an afterthought.

"There's no tough love between us," Royster said. "We all know that he's an exciting back to watch, and I'm excited to see him just like everybody else."

And yet, it's hard to overlook Royster's abbreviated rookie season when he ran for 513 yards and five touchdowns on 82 carries. That's why the 6-1, 212-pound sophomore is still listed as the starter and why he will likely earn the majority of totes even with Green and sophomore Brent Carter in the picture.

Still, with the Lions trumpeting a return to a spread offense, Green is sure to see his touches - possibly in the range of 13 to 17 per-game.

That may not be in the 20s, but it's more than 12 and definitely better than being green.

"My confidence level is high," Green said. "I'm prepared. I'm ready to go. I'm ready to contribute to this team and I want to help get this team to our goal, which is a national championship."

Contact staff writer Jeff McLane at 215-854-4745 or jmclane@phillynews.com.