The Royals and Expected Strikeout Rate

          The Royals experienced their first sweep of the season at the hand of the Yankees over the last weekend.  It is crazy that the Royals went this long into the season (midway through May!) without being swept.  After last year’s 12 game losing streak at the beginning of the season, this is welcome.  However, the Royals have lost 6 of their last 7 games.  I don’t think the Royals will sustain this kind of losing for long, though.

            

          Today’s post will be about strikeouts.  The Royals currently have a K% of 17.6%, which is good for 6^th in the MLB.  As I have written before, the Royals depend on contact for offense, not walks and home runs (like the aforementioned Yankees do).  I have already written about the strategic value of this strategy, but today I want to look at whether or not the Royals can be expected to continue their low K% ways.

            

          Mike Podhorzer over at FanGraphs published an article detailing a formula for a stat called “xK%”.  This stat stands for “expected K%”.  Podhorzer wanted to create an equation that given a player’s plate discipline statistics would produce an expected strikeout rate.  I applied his formula to the 9 lineup regulars of the Royals, and the results are here.

Name	Z-Swing%	Contact%	Zone%	K%	xK%	Difference
Alex Gordon	0.636	0.795	0.460	21.6%	19.5%	-2.1%
Lorenzo Cain	0.633	0.847	0.499	15.0%	14.7%	-0.3%
Billy Butler	0.623	0.855	0.424	16.1%	14.8%	-1.3%
Eric Hosmer	0.749	0.796	0.451	18.4%	16.7%	-1.7%
Salvador Perez	0.609	0.874	0.500	16.8%	12.9%	-3.9%
Mike Moustakas	0.702	0.808	0.400	13.6%	17.2%	3.6%
Alcides Escobar	0.646	0.861	0.472	9.3%	13.3%	4.0%
Jeff Francoeur	0.732	0.709	0.467	23.4%	24.7%	1.3%
Chris Getz	0.647	0.887	0.502	14.3%	10.7%	-3.6%

             

          The three variables in the equation are Z-swing%, contact%, and zone% (the three input variables are in decimal form for Excel calculation purposes).  I have previously written about contact%.  Z-swing%, in case I haven’t written about it before, is the percentage of pitches in the strike zone at which a player swings.  Zone% is the percentage of pitches a player sees inside the strike zone.  The equation that Podhorzer created has an R^2 value of 0.81, so the model is quite good, even with a small sample size.

            

          According to this model, several Royals players are actually striking out more than they should be.  Given that this research is still fairly new, explaining the differences between xK% and K% is difficult.  It is possible that random fluctuation is causing the difference, or it’s possible that the player in question has the ability to beat out the xK% consistently.  I think if these 9 players were closer to their xK% levels, the Royals might have an even lower K%.  The extra observed K% could partially explain why the offense hasn’t quite performed up to expectations so far.