And here are their MLB ranks for starter ERA- (ERA relative to league/park): 10, 2, 8, 25, 6, 12. All top-half in rotation run prevention except for the Padres. Try to filter the effects of defense (FIP-) and it looks even better, with even the Padres jumping up into the top half too. Also, as a group these are not bad teams, and their rotations generally weren't the reason for any missed expectations. Go to Fangraphs and sort team starter performance by FIP- or ERA- and then by K% -- they're not perfect matches, but they're close. BB% is a good match too, but also note that high K% seems to correlate pretty well with low BB% too. http://www.fangraphs.com/leaders.aspx?pos=all&stats=sta&lg=all&qual=0&type=1&season=2015&month=0&season1=2015&ind=0&team=0,ts&rost=0&age=0&filter=&players=0&sort=13,a If you're focusing too much on the BB% side of that correlation, as it seems the Twins have done at times, you are probably leaving a lot of effectiveness/predictability/stability on the table.