The rookie arrived midseason when an injury to a popular veteran created an opening. His play made the veteran expendable. But then came the dreaded sophomore slump as the youngster adjusted to life in the big leagues. Sounds like Will Middlebrooks, right? It does, except this story also belongs to Stephen Drew. In 2006, Drew made his big league debut for the Diamondbacks when Craig Counsell injured his ribs. Drew delivered, hitting .316 with an .874 OPS in 59 games and emerging as a key young player on an aging team that was about to retool. A solid fielder at short with some pop, Drew looked like a serious building block. But after Arizona jettisoned Counsell that offseason, reality hit hard. Given the everyday job at short, Drew wasn’t terrible by any stretch, but he wasn’t the dynamic force of 2006, either. He hit just .238 with a .683 OPS in 150 games, and suffice it to say, he knows what Middlebrooks is enduring at the moment. “That second year, man, I think that’s the biggest thing that Will’s going through right now,” Drew said yesterday. “The league has a lot of stuff on you. You’re making adjustments. Sometimes the ball doesn’t fall in your court. You’re hitting balls good and you get out. That’s just the way this game is. That’s why it’s a humbling game, and probably the hardest game to play.” Drew harbored no illusions that baseball was easy after his great start in 2006. With two older brothers who played in the majors, including former Red Sox right fielder J.D., he knew better than to believe he wouldn’t struggle. “Your first year, the league’s trying to find you out and you’re trying to figure them out and then it’s just one of those things, that sophomore kind of deal,” Drew said. “It’s a learning process for you, because the league has more info on you. Especially today, man, I mean all the daggum scouting reports and all the TV we have and advance reports, you’re out there.” Middlebrooks has learned that the hard way, particularly this weekend, when he lost his starting job to Jose Iglesias. It was only a year ago, after all, that Middlebrooks had done unto Kevin Youkilis as Drew did to Counsell in 2006.