The Diamondbacks fired former 2007 Manger of the Year Bob Melvin and are expected to replace him with A.J. Hinch, who is the club’s vice president of player development.

The 47-year-old Melvin’s firing comes after a disappointing start by the Diamondbacks, who entered Thursday 8½ games behind the Los Angeles Dodgers in the NL West. Melvin, who went 337-340 in four-plus seasons, had one year left on a contract he received after being the 2007 NL Manager of the Year.

Melvin’s stock rose when he guided a youthful but talented group to the NL West title two years ago. He was dismissed because many of the same players have failed to live up to expectations based on that season, when the Diamondbacks posted an NL-best 90-72 record despite being outscored by 20 runs across the season.

Speculation about Melvin’s future grew with every 1-2-3 inning by the Diamondbacks’ hitters. Arizona entered Thursday with a .225 batting average, by far the worst in baseball.

Arizona’s offense was a major question mark coming into the season, but as long as the pitching came through the D’Backs were expected to compete in a weak NL West. But Brandon Webb’s shoulder injury (and subsequent trip to the DL) was a crushing blow to the club’s starting pitching and the offense has been even worse than expected.

Melvin can’t do anything about Webb’s injury, Conor Jackson hitting .191 or Eric Byrnes averaging a paltry .139. But the reason he was inevitably fired is because the club has lost all emotion. It’s only May and the D’Backs are playing like it’s August and they’re 15 games out of first. Maybe the 34-year old Hinch can breathe some life into a club that certainly has talent, but is currently lacking any kind of desire.

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Offseason movement: The D-Backs made a couple of nice moves, including signing potential leadoff hitter and everyday second baseman Felipe Lopez, as well as free agent starter Jon Garland. They also added Tom Gordon and Scott Schoeneweis to help setup closer Chad Qualls. Randy Johnson, Orlando Hudson, Adam Dunn, Brandon Lyon, Juan Cruz and David Eckstein all vacated the desert this offseason.

Top Prospect: Jarrod Parker, RHP
Unlike other clubs that have a couple of players that could be viewed as top prospects, there’s no question that Parker is the best of the best in the D-Backs’ farm system. The 9th overall pick in the 2007 amateur draft, Parker stands just 6’0”, 175 pounds and is rather small in stature. But his fastball is dominating and has even drawn comparisons to Roy Oswalt, which is quite the compliment in itself. The 20-year old probably won’t get the opportunity to crack the big league roster for another year or two, but he could be quite the No. 3 behind Brandon Webb and Dan Haren as early as 2011.

The Big Question: Can this club make a postseason run without a dominant closer?
Chad Qualls will likely emerge as the Opening Day closer, but that doesn’t mean that it’s his job for keeps. He’ll have to continue to earn it throughout the season because Tony Pena, Jon Rauch and even Tom Gordon will have the opportunity to snatch the role from him if he starts to falter (much like they did this spring). The D-Backs are definitely a contender and could win the NL West given their young lineup and outstanding starting pitching. But will the lack of a dominant closer eventually sink them? Manager Bob Melvin can’t be worried about who will close out a tight ballgame in the ninth, so hopefully Qualls will not only keep the job all season, but also be steady and reliable.

Outlook: As soon as Manny Ramirez re-signed with the Dodgers, everyone and their mother was ready to hand the weak NL West over to the boys in blue. But people seem to be forgetting how good the Diamondbacks’ starting pitching is, and how good it can be. (Okay, well maybe people aren’t forgetting, but they certainly seem to be pushing it aside to drink out of the Manny Ramirez-Dodgers Kool Aid fountain.) Brandon Webb and Dan Haren form one of the best 1-2 punches in the NL and offseason addition Jon Garland won 14 games for the Angels last year. Throw in emerging youngster Max Scherzer and ‘Zona has the best rotation in the NL. The problem (and it’s a big one, which is why many believe L.A. is the team to beat in the NL West) is that the D-Backs’ lineup is pretty weak. It isn’t San Francisco Giants-weak, but weak nonetheless. Felipe Lopez isn’t an upgrade over Orlando Hudson and while Chris Young and Justin Upton have loads of potential, neither of them even sniffed a .270 batting average last season. The lineup is full of holes and strikeout artists and losing Adam Dunn cuts down on the power production. It’ll be interesting to see which team emerges in the NL West this year – the offensive-friendly Dodgers or the pitching-stacked Diamondbacks. We’ll go with the pitching and say ‘Zona comes out on top.

Projection: 1st NL West