March 1, 2013 5:22 PM

Confident Herrera working to add improved curve to his power arsenal

Royals reliever Kelvin Herrera established his bonafides last season by compiling a 2.35 ERA in 76 appearances after pitching his way onto the club as a rookie in spring training. He can push the radar gun to 98-100 mph but now has made honing his curveball as his chief goal this spring.

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