Yokohama Clubhouse?

I've looked at the Wikipedia article in question, and I'm baffled as to where such a statement came from. But looking at the Discussion section, it clearly states that the page has not yet been peer reviewed, so I'd guess that it is may or may not be true.

I've only been into the underbelly of Yokohama Stadium one time, and there are a lot of doors leading off of the main corridor that leads to the benches. Any one of them could well be a "clubhouse," depending on your definition. What would your definition of "clubhouse" be, by the way? A shower room? A locker room? A meeting room?

I'm not aware of any other facilities anywhere near Yokohama Stadium. That doesn't mean they don't exist, just that they aren't publicized.

The main facilities for the ball club (dormitories, indoor, and outdoor practice facilities) are located in Yokosuka, at least one train transfer from Yokohama Stadium. So I wouldn't call that "near the stadium" by any stretch.

Looking at the Japanese Yokohama Stadium Wikipedia page, I see it mentioned that the Yokohama Marinos (soccer) practice ground and clubhouse is nearby. This may be the source of the statement, but I cannot be sure.

I'm betting they're thinking of Jingu, actually? Yakult has a clubhouse of sorts outside the stadium, and the players come into the stadium an hour or two before gametime; if you know where to stalk at the right time you can usually see Swallows players riding their bikes over or walking from the clubhouse building to the gate that lets them in (the walkway between the infield and outfield parts of Jingu). I don't know exactly what facilities are inside Jingu, but I've been led to believe they're not particularly extensive; the college teams that have buses generally just have their players grab their stuff and run onto buses after the game rather than even changing out of their uniforms at the stadium.