If you are baseball fan and looking forward to watch baseball game in Tokyo metropolitan area, Saitama Seibu Lions' game is an ideal team to choose.
There are two reasons to choose Lions.
1) Their stadium is roofed and game to be cancelled is rare.
2) Lions tickets are easier to get than Giants.
At first, Japanese baseball stadiums have two types. First, open air. Which means match can be cancelled due to bad weather even rainfall. Then, roofed. Which means cancellation is rare. Only it can happen to extreme bad weather including typhoon - in this case public transportation will be suspended too. Therefore, it is better to choose roofed stadium if you are staying in Japan for a short period.
Then, there are five teams in Tokyo metropolitan area including Lions. Lions and Marines belong to Pacific league and the other three teams belong to Central league. Apparently, Central league attracts more spectators than Pacific league which means tickets for Pacific league is easier to obtain.
Marines' stadium located in Chiba is not roofed and Central league's only roofed stadium in Tokyo metropolitan area, Giants is the most popular team in Japan, which means tickets are hard to get.
Anyway, Lions are not weak team at all. Lions were 23 times Pacific league champion and also 13 times Japanese champion. Therefore you can enjoy the top level game in Japan.
By the way, Lions' stadium, Seibu Metlife Dome is located in Tokorozawa, Saitama prefecture. You can reach the stadium by Seibu railway trains from Ikebukuro station including limited express operated exclusively for the games.