TAMPA, Fla. -- As Joba Chamberlain threw a bullpen session Saturday morning at Steinbrenner Field, a very interested spectator watched from an adjacent pedestrian bridge.

The onlooker was Harlan Chamberlain, Joba's father. He was watching to see if Joba had recovered from an oblique strain. "When he was warming up, I looked at his face," Harlan said. "I didn't look at his mechanics. And when I saw him smile, I knew he was fine."

He sees something else when he looks at Joba: maturity. That could be as important as the speed of Chamberlain's fastball as he begins what appears to be a crossroads season with the Yankees. "I look at it as kind of a coming out as far as his maturity," Harlan said. "He's been through one hell of an ordeal in four years. I mean, it's been so many peaks and valleys. He's approached this year with a renewed enthusiasm. He's matured."

As Joba, 25, enters his fifth major-league season, he no longer is the flame-throwing eighth-inning phenom or a projected top-of-the-rotation starter. He's a middle reliever.

The Joba Rules are a thing of the past. The door on the starter/reliever debate has been slammed shut by general manager Brian Cashman, who refused to let him audition for the rotation even after the Yankees missed out on Cliff Lee and Andy Pettitte retired.

In a way, Harlan says, that certainty is a good thing for Joba. Coming into camp for the first time knowing what is expected of him has made it easier for him to focus on becoming a better pitcher. "When he first came up in '07, I said, 'Son, this is awesome,' " Harlan said. " 'Your success, it's [almost] iconic, and people are going to expect that. You've set your standard at a very high level and people are going to want to see that continually. I'm going to tell you right now: It's not always going to be there. You're going to have to weather that time.' And he has.

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"As a father, I'm kind of torn between two things. I can appreciate all his accolades as far as athleticism and as a pitcher -- and don't get me wrong, I'm very proud of that. But what I'm even more proud of is the person that he's grown to be. He's done a lot of growing in such a short time and at such a young age."

That's not to say Chamberlain hasn't had his public stumbles. He was arrested and charged with DUI in his hometown of Lincoln, Neb., in October 2008. He pleaded guilty in April 2009 and was sentenced to nine months' probation.

"I don't preach to him about it," Harlan said. "I just tell him from time to time, 'Be responsible.' What any father would tell his son or daughter. Now that's the least of my worries."

What does Harlan worry about most? For now, that Joba doesn't try to come back too fast after the bullpen test, which he passed. And that he can live up to being Joba Chamberlain of the Yankees. "He's fully aware," Harlan said. "But he's still growing. I'm 59 years old and I'm still growing."