A look at Joey's batting line this year indicates that he's having a terrific year, posting a .423 wOBA and a 165 wRC+. That's phenomenal production, and the point of this piece is not to complain.
But what is interesting is how he's done it: last year, he hit .324/.424/.600. This year, he's hit .330/.463/.515. His ISO is down from .276 last year (and .245 in 2009) to .186 this year. His walk rate is up (20% vs. 14% last year), and his strikeout rate is down (18% vs. 23% last year). His HR/FB ratio is 12.5% this year, down from 25% last year and 19% career.
I see three possible explanations for this.
1. Pitchers just aren't giving him anything to hit, so he's walking and isn't able to use his power as much as he has in previous years.
2. Votto has changed his hitting approach, being more selective, and trading power for getting on base.
3. It's just a random fluctuation and is not the result of a specific cause, per se.
I think all three could well be true. Here's a quick look at each:
1. Pitchers just aren't giving him anything to hit.
While there are open questions as to its accuracy, FanGraphs' Zone% statistic shows no difference between last year and this year in the # of pitches Votto has seen in the strike zone (42% both years).
He has been seeing more change-ups (15% vs. 10% last year), and fewer sliders (13.5% vs. 16% last year) and curve balls (8% vs. 10% last year). That could be a function of the # of LHP's vs. RHP's he's faced, however. This year, 78% of his PA's have been against righties, while last year it was 64% (which seems like a huge difference to me--have we lost some lefties from the division or something?). Pitchers use change-ups more commonly against opposite-handed hitters, so that makes sense. So, perhaps pitcher's aren't pitching him differently, per se, but the fact that he's seen more righties means he's encountered different pitching than last year thus far.
2. Votto has changed his approach
Votto is showing indications that he's become more patient, and making better contact. He's only swinging at 25% of balls out of the zone this year compared to 30% last year, and what's more is only swinging at 67% of balls in the zone compared to 73% last year. When he does swing, he's making better contact, with a 2% improvement in contact out of the zone, and a 3% improvement in contact in the strike zone (3% improvement overall). What the data don't tell us is why he's making better contact: is he just being more selective, or is he trading power for contact by not swinging as hard?
Other thing: last week, I remember hearing some announcer say that Votto was a little bit banged up. I haven't heard anything else about it. But there is always the possibility of a hidden injury that is affecting his power production as well.
3. It's just a random fluctuation
The effects on his batting line could still be a random fluctuation. Votto has just shy of 250 PA's right now in 2011. Based on work from Pizza Cutter, we can expect things like his swing rate, contact rate, strikeout and walk rates, and ground ball rates to stabilize (by which I mean about 50% signal or better, as opposed to a majority of noise) by 250 PA's. But more general measures of batting performance, like OBP, SLG, and ISO do not provide the same level of stability until you get into the 500-550 PA range. So while I think some of the approach changes in #2 may be (at least in part) real, the ultimate effect it will have on his power, in particular, may not yet be apparent.
So, the answer may well be all of the above, though there was less support for #1 than I expected to see. Regardless of what's behind it, Votto is continuing to post phenomenal numbers as the cornerstone of the Reds' offense. While I would certainly love to start seeing more home run power from him, it's impossible to get upset when a guy is OBPing .463. The Reds are lucky to have him.