No no no. You dont have to clean your Wii. Just the disk. I did this and I havent encountered the glitch since:

1. Take a cotton ball (or some lint free cleaning cloth) dab it in some water.
2. Clean the back of the disk (the non labeled side) with it (make sure the towel/cotton ball isn't FULL of water. Just a bit wet. And make sure ur not using anything else but water.) Avoiding the rim of the disk.

3. Allow the disk to Air Dry, once it is completely dry, re-insert the disk into the Wii. And play the disk.

This guide was by Nintendo actually. But, I just put it in my own words :)

It's probably your internet connection.

It's most likely your internet connection. You need a fairly fast connection, sorry DSL users, it's time to upgrade.

It's your internet connection, most likely
if it's only freezing during online play then your connection is getting dropped, and the getting stuck in a wall was just bad luck, it happens to everyone

Same here but i dont relly care

If an online match spawned you in a wall, you probably started the match past a certain "spectator point" in which the game will only let you watch until the match is over. This has happened to me before. I think the game just encountered a glitch due to your connection (the Wii's fatal flaw...). If this happens again, just wait until the round is over and play in the next one.

Easy keep your remote pointed at the screen at all times. Its worked for me countless of times.

Spawn glitch
two ways to fix (kind of)

Mash A and 1
Make sure the cursor is on the screen when the match is loading and keep it there
Internet connection has nothing to do with it, as does the disk.

It's a spawn glitch. It's the game developers' fault, not the system's or the disc's for being dirty. Just faulty programming.