|Scott Diamond is nowhere near|
the leaderboard in groundball
rate this season.
But it's quite obvious that even at his best — his best being 2012 — his margin of error is thin.
In 2012, he was at the top of the league in avoiding walks, very close to it in ground ball rate. By being the best in the league at what he was good at, he could overcome his significant weakness in strikeouts.
In 2013? He's a bit better than average in getting grounders, a bit higher than that in his walk rate. And his strikeout rate has gotten worse — he's fallen off to about half the league rate in strikeouts.
He's exceedingly unlikely to ever approach league-average in strikeout rate, which I am becoming increasingly convinced is the most important figure in pitching. And that means league average or a little better in control and groundballs isn't going to cut it for Diamond.
So why do I still have hope for him? He's lefthanded. He's intelligent. His BABIP — batting average on balls in play, a measure of, depending on one's view of the stat, either of how much his defense is helping him or how lucky/unlucky he is — would be one of the 10 highest in the league if he had enough innings to qualify. (In 2012, his BABIP was almost exactly average.)
But the underlying point remains: For Diamond to be successful, he has to be the best at what he's good at. That's a high hill to climb, and a status difficult to maintain once achieved.