Load Up on Right-Handed Bats

Wednesday, May 02 2012 @ 10:27 AM EDT

It's typical practice for major league teams to give some left-handed batters a rest when the opposition starts the game with a left-handed pitcher on the mound. This, of course, is because of the well-known platoon advantage that pitchers have against same-handed batters. I remember a time when it was rare to see any left-handed batter in the lineup against Randy Johnson, but we don't seem to have a monster like that in the game today. Most managers will leave their best lefthanded bats in to face a lefty starter, with the more marginal lefty bats replaced by right-handed hitters.

But not all pitchers are created equal, especially when it comes to this theoretical platoon edge.

One thing to note is that left-handed starters tend to have a smaller platoon differential than left-handed pitchers at large. I believe this is because managers are aware that the opposing team can stack their lineup with righties and tend to select left-handers with a smaller platoon split to be their starters.

Makes sense, I think. Here is a table of the current left-handed starting pitchers in American League rotations. I count 20 of them (I don't include those on disabled lists):

2009 to 2012			wOPS
			(regressed)
	%RHB	Total BF*	vLHB	vRHB		split
F LIRIANO	77.1%	2087	0.230	0.264		-0.034
B MATUSZ	78.8%	1306	0.249	0.277		-0.028
D HOLLAND	76.2%	1832	0.238	0.264		-0.026
M HARRISON	71.9%	1488	0.235	0.258		-0.023
D PRICE	76.9%	2439	0.211	0.233		-0.023
CJ WILSON	76.5%	2211	0.207	0.228		-0.021
D DUFFY	74.5%	541	0.262	0.282		-0.021
C SABATHIA	75.1%	2897	0.214	0.230		-0.016
J SANCHEZ	76.5%	2029	0.226	0.242		-0.015
B CHEN	71.6%	1626	0.245	0.256		-0.011
WY CHEN	77.1%	105	0.233	0.243		-0.010
J VARGAS	74.1%	2176	0.234	0.243		-0.010
F DOUBRONT	64.6%	254	0.263	0.271		-0.008
J LESTER	74.5%	2608	0.224	0.230		-0.006
C SALE	60.0%	502	0.215	0.221		-0.006
D SMYLY	75.6%	90	0.235	0.239		-0.004
T MILONE	86.0%	229	0.238	0.240		-0.002
M MOORE	77.7%	148	0.255	0.256		-0.002
J DANKS	71.4%	2552	0.240	0.240		0.001
R ROMERO	71.0%	2678	0.259	0.227		0.032
unweighted average	74.4%		0.236	0.247		-0.012
* BF is approximated here as AB+W+HBP
wOPS is (1.75*OBP+SLG)/4

Some brief commentary: I have used all major league data from 2009 to the present (which excludes Japanese League data), sourced from espn.com. The regression is based in part on the recommendations of Tom Tango in his book The Book. The second column denotes the percentage of total PA that right-handed batters account for versus the given pitcher. I am fairly confident in the accuracy of regressions for pitchers with over 2000 BF; those with under 1000 BF should be taken with a spoonful of salt.

One of today's starters, Matt Harrison, has a slightly greater than normal platoon split for this sample. The other, our beloved Ricky Romero, is an altogether different breed. Romero has the largest "wrongway" split of any left-hander I've come across. At least some of the teams seem to be aware of this, as Romero's RHB faced% is 71%, versus the sample average of  74.4% - indeed it is the lowest among the pitchers listed above with a substantial number of batters faced.

It will be interesting to see if Ron Washington starts either (or both) David Murphy and Mitch Moreland this afternoon. If he does, it will be an indication that he is aware of Romero's odd righty-lefty characteristics.

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