Norichika Aoki’s (Relatively) High Strikeout Rate


Mandatory Credit: Brad Rempel-USA TODAY Sports

When the Royals traded for Norichika Aoki this past December, the organization praised him as a “true leadoff hitter,” – a term I abhor, for various reasons, none of which are relevant at this time – and someone who made solid contact and could get on base. He could handle the bat and also cause some havoc on the basepaths. Aoki was a good hit-and-run type of hitter, because he didn’t swing and miss much, which also meant he didn’t strike out much.

What happened to that Nori Aoki?

In his first two seasons with the Brewers, Aoki struck out in just over 7.5% of his plate appearances, the second lowest percentage among all qualified hitters during that time. In his first 19 games with the Royals, Aoki has struck out 15 times, and has a strikeout rate of 18.1%. It doesn’t take a math major to see that 18.1 is quite a bit higher than 7.5.

In 2013, Aoki didn’t get his 15th strikeout until June 16th. In 2012, his 15th strikeout came on June 3rd. After a quick glance at my calendar, I see that Aoki’s 15th strikeout in 2014 happened on April 23rd.

Before I delve any deeper, I do want to once again point out that these statistics have been accumulated in just 83 plate appearances, and I think it’s more likely that Aoki’s strikeout rate will regress to the mean at some point this season. Additionally, despite the current spike, Aoki still has a strikeout rate below the league average, so it isn’t like he’s turned into Drew Stubbs. It is interesting, however, to see a player with elite bat control have so many issues making contact thus far. Small sample size or not, the numbers are fun, at least for a nerd like me.

Obviously we see what’s been happening. I’d like to try and find out how it’s been happening. That is, what about Aoki’s offense has changed this season to result in so many strikeouts?

First, we see that Aoki is swinging at more pitches this year, both in and out of the strike zone. In his first 2 years, his O-Swing% was less than 22%, but this year it’s above 25%. It’s a similar story with his Z-Swing%, though to a lesser extent, as he’s swinging at 61.4% of balls in the zone this year, compared to just over 60% in the previous 2 seasons. Put them all together, and Aoki’s Swing% is a full 2 percentage points higher this season.

Swinging at a higher percentage of pitches can be acceptable, if it’s combined with a higher contact rate. Unfortunately for Aoki, that has not been the case in 2014.

This year, Aoki’s Contact% is at 86.4%, which is significantly lower than what he had posted in Milwaukee. Part of that is due to a lower contact rate on pitches in the zone (92.8% this year, roughly 93% previously), but most of his contact problems have been on pitches out of the strike zone. Prior to coming to Kansas City, Aoki had O-Contact% of 77.0% and 83.3% in 2012 and 2013, respectively. Today, Aoki’s O-Contact% is currently at 68.6%. Aoki is one player who can take advantage of weak contact on those pitches out of the zone, because his speed can create opportunities for infield hits. Not making contact on pitches does not create those opportunities.

In total, Aoki’s swinging strike rate is 6.1%, which is about 185% higher than it was in 2013 (3.3%). That’s kind of a lot.

If these numbers aren’t making much sense, perhaps I can present some pretty pictures showing Aoki’s whiff rate. The first image is from 2012-2013.

Most of those boxes have smaller percentages, and the only somewhat troubling spot is below the strike zone on the outer half. Even though there is a red box and a few purple ones, the actual whiff rates aren’t terribly high. Now, let’s take a look at this year’s sample.

Yikes. Again, this is a small sample, but Aoki has swung through 3 pitches in the middle of the plate already, after having a total of 11 swings and misses in that spot in the last two years combined. He’s also missed a fair amount of pitches below the strike zone, which doesn’t help matters.

As for the specific pitches giving Aoki the most trouble, I’m hesitant to rely too much on pieces of an already small sample, but it does appear that breaking balls and offspeed pitches have been tougher for him to handle this year. He has a slightly higher whiff rate on fastballs than he had in previous years, but just by a few tenths of a percent, so I don’t think that’s anything to be concerned about.

We now know the what and the how, so of course the next question is: why are these things happening?

To be honest, I don’t know.

Aoki is 32 years old, meaning he could be entering his decline phase, but I have a hard time believing he’s lost so much of his contact ability in less than a year. There could be some kind of adjustment period for a player switching leagues, although that can be difficult to gauge, and it’s normally more prevalent in pitchers coming over from the National League. Aoki has drawn walks at his career rate, if not a bit higher, so I think his pitch recognition skills are still there. My only guess for an explanation at this point is related to his mechanics.

I’m not a swing coach, but I do wonder if Aoki’s timing is slightly off. He has that big flamingo kick when he starts to load, so if his foot doesn’t come down early enough, his hands may not have enough time to get down to the low pitch he’s struggled with so far. That doesn’t really explain the whiffs in the heart of the plate, but it could be a contributing factor.

As I mentioned, I’m not quite sure what the underlying cause is, but it has been crazy to see Aoki’s strikeouts spike in the way have this season. I don’t think it’s time to worry about him just yet, of course, and even if he doesn’t get back to the contact ability he had in Milwaukee, I still fully expect him to at least get close to that. It may require some adjustments, but Aoki’s other stats have been encouraging, meaning a few less strikeouts should propel him back to the level of production the Royals were hoping to see when they acquired him.