wRC+ and Handedness: The Importance of Being Lefty

I think we’re all aware that the lefty vs. righty matchup favors the batter.  But to what extent?  And what are the implications?  Prepare to be inundated with a bunch of charts and tables.

For the purposes of this article, I’ll be sticking to using wRC+, my favorite all-in-one, level-playing-field batting stat.  My sample consists of all batters from 2002-2012 who had at least 200 total PAs against lefties and at least 200 more against righties.

The charts in this article will break down the frequency distributions of wRC+ for left-, right-, and switch-hitting batters, grouped to the nearest multiple of 10.  For example, the chart below shows that 21.5% of right-handed batters (RHB) hit for over 85 but less than or equal to 95 wRC+ against right-handed pitchers (RHP).

(Mouse over or tap image to see splits against LHP, Left-Handed Pitchers):

“BHB” is what I’m calling switch hitters (Both-Handed Batters).  In my sample, by the way, there are 193 LHB, 386 RHB, and 104 BHB.

	Average wRC+				PA-Weighted Averages
	RHP	LHP	Overall		RHP	LHP	Overall
LHB	110.0	84.9	103.8		114.0	91.3	108.1
RHB	88.8	107.5	94.8		96.3	112.2	100.8
BHB	94.0	90.4	93.3		100.7	98.1	100.0

Now, looking at the overall numbers, you might be tempted to say that being a left-handed hitter is a pretty big advantage.  Well, considering over 72% of all batters’ PAs are against right-handed pitchers, that would make some sense.  But then again, switch hitters hit lefty too… maybe it’s just that lefty batters of late were simply better hitters.  And, who knows — maybe switch hitters generally lack the experience hitting as a lefty that true lefties have… or maybe, a lot of the time, it was being a more marginal talent in the first place that led them to learn switch hitting.

	% of PA vs. RHP	% of PA vs. LHP
LHB	74.2%	25.8%
RHB	71.4%	28.6%
BHB	72.0%	28.0%

Instead of looking at how whole groups of batters fare overall, let’s look at the differences within individual batters.  In the next graph, you’ll see the distribution breakdowns of hitters’ wRC+ against righty pitchers subtracted by their wRC+ against lefties.  Sorry, no mouse-over surprise for this one:

For the following table, the PA-weighted averages go by whichever PA count is smaller — vs. RHP or vs. LHP (which pretty much is always vs. LHP).

wRC+ Against RHP Minus wRC+ Against LHP

	Average	Standard Deviation	PA-Weighted Average
LHB	25.2	21.3	25.7
RHB	-18.7	20.8	-17.7
BHB	3.6	23.2	2.8

It’s probably a little more apparent in the table than the graph, but I’d say recent lefty batters legitimately have shown themselves to be more affected by the handedness of the pitcher, for whatever reasons.  If you refer back to the first table, you’ll see that, in particular, lefty batters suffer more against LHP than righties do against RHP.  To further explore that avenue (mouse over or tap for LHP, again):

                        Average wRC+ Differentials

	RHP-Overall	LHP-Overall
LHB	6.2	-18.8
RHB	-5.9	12.6
BHB	0.7	-2.8

                                Standard Deviations

	RHP-Overall	LHP-Overall
LHB	5.5	16.4
RHB	7.4	14.0
BHB	6.5	16.8

What you’re seeing here of course has a ton to do with the aforementioned fact that hitters generally face righties more than 70% of the time, which skews their overall numbers in that direction.  But just keep these differences in mind as a rough adjustment to make to a batter’s wRC+

However…

There are major, real differences between hitters in how well they handle opposite-handed pitching.  How consistent a player is in this regard, vs. how much you can expect them to regress to the mean, is a topic for another article.

For now, here’s a sortable list of the discrepancies between batters’ wRC+, in terms of RHP minus LHP (R-L) and in terms of Opposite minus Same-handed pitching (O-S).  You should be able to change the “200” you see as the minimum plate appearances to whatever you’d like, and it will filter the list (just re-sort after changing it).

Discuss Amongst Yourselves

So, it seems pretty clear that recent lefties have benefited a little bit more than righties when facing opposite-handed pitching, but suffered considerably more when facing same-handed pitching.  Since a lefty batter has plenty more opportunities to face opposite-handed pitching, the net result benefits them… but still, how can we explain why their fellow lefties give them such problems?  Is it relative lack of exposure to lefty pitching?  Could umpire strike zone differences have something to do with it?  Facing more specialist relievers?  Let me hear your thoughts, and maybe we’ll get a follow-up out of this…