The following suggestions are definitely NOT from an expert; I'm trying to figure out some of the same things you are...
1. use a faster shutter speed to stop the action, even though the result will be underexposed. You can brighten those images surprisingly well in almost any image editor. An editor that supports "levels" will do the best. PhotoShop Elements (under $100, sometimes on sale for $50) or Paint Shop Pro (also under $100) are both good choices.
2. for even better post-processing, consider buying Applied Science Fiction's "Digital SHO" plug-in for $49. (It works with PhotoShop-compatible products.) The website is
http://www.asf.com but they recently were acquired by Kodak. Their home page lists two versions of SHO: at the top of the page is the Professional one for $100 or so; the original is further down. (I've been using the $49 one for a couple of years and the company's name is not exaggerated.) There are other tools like this available, and some of them may be as good or better, but I haven't tried them and can't give an opinion about them.
3. if you are allowed to use a flash at the game, try an external flash. You may be too far away from the players for even an external flash to do much, but it may help a bit. At least, it'll supplement the available lighting.
4. remember that higher ISO's produce noisier (grainier) images. The camera's CCD has a fixed sensitivity, so raising ISO is not like changing from ASA 100 film to ASA 400 film. All the camera does is to amplify the signal more than normal, and that emphasizes the noise. Post-process brightening in an image editor (via LEVELS or SHO) can give you higher quality results because the computer has a far more powerful CPU and a lot more time to do a good job than the camera has.
5. you can raise the EVF's brightness on the SETUP menu for better visibility when composing the shot. This does not affect the captured image.
If possible experiment in advance at home with faster shutter and/or lower ISO's, so you won't wind up using unacceptable combinations at the games.
And, as others have said, you had several very good pictures in there
--
Charlie Howard