Over the past several years Carlos Zambrano has been the keystone to the Cubs starting rotation, leading the group as the ace since the days of Mark Prior and Kerry Wood.

The fact of the matter is that Zambrano hasn’t posted an ERA under 3.50 since 2007, and for a “power pitcher,” he has only exceeded 200 strikeouts twice in his seven year tenure as a starting pitcher.

Zambrano has always dazzled fans with both his electric fastball and temper, but the fastball that reached the mid-90s and posted positive win values each year of his career is showing signs of decline.

Zambrano’s fastball is averaging 90.9 mph, down from his career average of 92.1. He is also throwing it 52.4 percent of the time, far down from the 62.7 percent last season, as well as the +70 percent seasons of 2003-2005.

Correlating with the decline of fastball use is the increased use of his split-finger fastball, which has been just a slightly above-average pitch, contrary to popular belief.

The fastball, once a plus-plus pitch is currently posting a run value of -7.0, easily the worst of his career.

Perhaps one reason Lou Piniella chose to pitch him out of the bullpen was to focus on his fastball more, and less on his secondary pitches.

Moving forward, Zambrano is owed $17.87 million this year and next year, $18 million on 2012, and holds a player option for $19.25 million in 2013 if he receives Cy Young consideration, according to Cot’s Contracts.

Zambrano has to be a starter for the Cubs to get the most value out of him, and his contract, and he must focus on improving his fastball in order to succeed in the coming seasons.

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