Monday, May 11, 2015

More on the strikeout rate

Trevor May walked
three and struck out
four in four innings
The Monday print column grappled in large degree with the conflicting indicators for Mike Pelfrey and Kyle Gibson, who each have very good ERAs with very poor strikeout rates and strikeout/walk ratios.

I have for years referred to strikeouts per nine innings (K/9) and strikeout-walk ratio (K/BB) as the leading indicator stats for pitchers. Given a choice of pitchers, I'd rather have the guy strong in those ratios than in ERA, because they are better predictors of future ERA than ERA itself.

The Twins so far -- roughly one-fifth of the way through the season -- have used six starters. Gibson and Pelfrey have been in the rotation throughout, as has Phil Hughes. Trevor May joined the rotation in the second go-around, Ricky Nolasco spent some time on the disabled list and Tommy Milone, who opened the year in the rotation, is now at Triple A.

Of those six, only May and Hughes have good strikeout rates and strikeouts per walk. Culled from Baseball Reference in the early morning today and ranked by K/BB:

Hughes: 6.5 K/9. 8.00 K/BB
May: 6.9 K/9, 4.00 K/BB
Pelfrey: 4.2 K/9. 1.23 K/BB
Milone: 5.2 K/9, 1.18 K/BB
Nolasco: 4.8 K/9. 1.17 K/BB
Gibson: 2.7 K/9. 0,73 K/BB

The American League averages, for comparison: 7.4 K/9, 2.43 K/BB. So even May and Hughes, with easily the best strikeout rates in the rotation, are below league average in striking hitters out. (The league average includes relief pitchers, and their strikeout rates are higher, so May and Hughes aren't truly subpar in that category.)

I for years regarded the K/BB ratio as the more important of the leading indicator stats. I've become largely convinced, as strikeouts have mushroomed, that K/9 is now a bit more important. But either way, the bulk of the Twins rotation lags in these important predictors of future results.

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