When Cuban defector Yoslan Herrera signed with the Pirates for $1.92 million in the offseason, the Pittsburgh brass knew his secondary pitches were all more or less in the rudimentary stages of development.

But Herrera’s struggles in his last start–he allowed four runs on seven hits over four innings on Tuesday–had little to do with the sharpness of his curveball or slider or even the depth to his changeup or the bite on his splitter. For the 25-year-old righthander, it’s about learning to attack with his fastball, especially commanding it over the inside part of the plate.

“He’s had some difficulty adjusting to using his fastball consistently,” Pirates farm director Brian Graham said. “He’s got to understand the value of establishing his fastball, which is a different mentality than he’s been used to.

“He wants to use all his pitches, and that’s fine–he’s got a solid five-pitch mix he can throw for strikes. He just needs to use the fastball more often to be more effective.”