Zack Greinke eased up on his slider use because he felt it hurt his elbow:

In the clubhouse across the way, Zack Greinke has pitched past 2,000 innings. His pitching arm bears no scars. He, too, stands fairly firmly against regrets. Several years ago, when it was still his best pitch, Greinke simply stopped throwing his slider so much. He’d leaned heavily on the slider, even won a Cy Young Award riding it and his fastball, and then he’d go to bed with his elbow feeling somewhat “different,” he said, or wake up the next morning that way, and one day decided this wasn’t the best way to a long and successful career.

Greinke, being Greinke, was perhaps just self-aware enough to change. He still throws plenty of sliders, but hopes to cap them at 15, maybe 20, per start, thereby balancing his desire to win with the hope to pitch again in five days. Perhaps the ulnar collateral ligament goes a thread at a time, he doesn’t really know, but if so, he was going to budget his threads, and not pitch straight through his elbow by the time he was 30 and then be no good to himself or his team for a year.

This reminds me of the joke about the guy who goes to a doctor and says, “Doc, it hurts when I do this.” The doctors says, “Don’t do that.”

In the course of a game, many different types of pitches are thrown. I’m not quite sure how one figures out which one is causing the discomfort.