How come Akinori Iwamura's power does not translate to the MLB?

I don't think any Japanese player has been able to translate their full power to MLB. Bigger parks are one reason, but it seems that NPB parks have gotten bigger over the years as well.

It looks unlikely that Iwamura will start hitting for more power. The Rays keep stats on fly ball average and noticed that when he hits the ball in the air Iwamura has a terrible average. So, they are encouraging to hit more line drives and balls on the ground. I don't think he'll ever reach double figures in HRs, let alone 44.

-How come Akinori Iwamura's power does not translate to the MLB?

As tigersgoredsox has pointed out, Meiji-Jingu Stadium [Baseball Reference], is a lot smaller than Tropicana Field [MLB.com]. It's most likely than Iwamura will top out as a gap hitter with doubles power in MLB. Also, not to mention there's the adjustment to MLB, the adjustment made by the pitchers who in the same division numerous times a year, and the scouts who montior the weaknesses and stregnths of MLB hitters.

Now a case of where some trace of power has been transfered to MLB from NPB, in is the case of Hideki Matsui [Baseball Reference] who has seasons of home runs amounting 20+ in 3 years: 04(31), 05(23), 07(25). The question is how did Matsui manage to transfer some of his power from NPB to MLB? Well, the Tokyo Dome [Japan Baseball Daily] and the old Yankee Stadium [Wikipedia] have similar dimensions. Can anyone out there among the Japanese Baseball faithful make any deduction as to why Matsui has transfered some power to MLB from NPB why others have failed at doing so?

Many hitters change their approach at the plate when going from NPB to MLB as well, becoming more contact hitters than they were in Japan. This is also because many of the hitters batted 3rd or 4th in the lineup while in Japan, but got moved up or down the lineup in the States. Not sure which came first though, kind of a chicken and an egg.

With Matsui, Yankee Stadium would seem to favor him. I need confirmation, but I'm pretty sure the old Yankee Stadium had a short right field fence that favored lefties. He should be able to take advantage of the home run-friendly new stadium, but I think his injuries of the past few years will sap a lot of his power.

Simon (number9) is right that Iwamura became more of a contact hitter when he became the lead-off hitter for the Rays. His main objective was to get on base and steal bases like Ichiro.

Can someone tell me why Iwamura is not batting lead-off this year? Upton is currently batting .190.

What about the balls? During the WBC I heard the Japanese commentators talking about the baseballs used in MLB which were more slippery and didn't go as far as the ones used in Japan.

A couple of reasons why, the stadiums are smaller in Japan as stated earlier and the balls have more life. You can see that if you saw the games last year when Boston and Oakland opened the season here. They used Japanese balls in a couple of the games and practice and balls were flying high off the signs in the outfield. Also most Japanese hitters have a different style of hitting. Most left handed hitters have a bailing/running type swing which in the MLB doesn't translate to power. Matsui had the most success because he has more of an American style swing with not much bailing out with the lower half.

- You can see that if you saw the games last year when Boston and Oakland opened the season here. They used Japanese balls in a couple of the games and practice and balls were flying high off the signs in the outfield.

Simply not true. What would be the reason for using Japanese balls in MLB regular season games?

Most likely balls from the pitching team were used, so MLB teams would've been using MLB balls when on defense.

As for stadiums, with the expansion of Jingu and the new Hiroshima Stadium, the only stadiums left in NPB that could be called "small" when compared to MLB counterparts are Yokohama Stadium and Tokyo Dome (lack of power alleys).

Source: Japanese Ballparks are Bandboxes - Truth or Myth?

Tokyo Dome is an extremely hitter friendly park. I have seen quite a few players who barely hit home runs in games hitting signs in Tokyo Dome in batting practice. It's probably the easiest park to hit home runs in Japan.

I am curious to know how big of a difference the balls are. I heard quite a lot of talk about this on WBC. I am not really sure about this, but I think the size is the same and weight, but the Japanese balls are easier to grip due to the way it is stitched, therefore the balls carry further? From a pitchers perspective the balls are more slippery, harder to grip due to the stitches?

You also have to keep in mind, Iwamura set the Central League record for strikeouts in 2004, the year he hit 44. He'd never come close before (23), and the closest in Japan he came since was 32, so it was something of a fluke-ish season.

Also, the all Central League's Parks in 2004 were in general smaller than most U.S. parks:

Average CL dimensions (Tokyo D, Jingu, Yokohama, Nagoya D, Koshien, Hiroshima Shimin)
95m/312ft
114m/373ft
119m/392ft

To infimum question, they didn't use it for the MLB games, but did use them for the warm up games with the Tigers and Giants and in batting practice when they played those games.

And to n26, all balls are made different. Some are a little bit smaller and/or can have higher seems (as what was talked about being slippery) or even harder than other balls. This is a world wide thing, it's hard to make balls in a consistent nature. It's been documented for years that Americans and Japanese use different balls and neither group seems to like the others balls. Lol (that sounds a bit funny).

To me it just seems that Iwamura has adjusted to the kind of pitching he faces in the American League and has shortened his swing. He doesn't want to strike out 200 times a year and I applaud him for that. His diminished power is not a bad reflection on Japanese baseball in any way. It just confirms that the typical Japanese player is smart and team oriented and does what is needed to win.

1. Parks are much bigger and less HR friendly
2. Different role on his team
3. Much different approach at the plate

It actually speaks volumes about how talented Iwamura is that he was able to transform his game to such a degree in order to adapt to MLB.