Blocking Spammers?

I have an Arsenal FC blog with wordpress, but I keep getting spam from rival fans who keep on posting spam. At the moment when I log on ever couple of hours into the site I have 10/20 comments to moderate.

It’s getting tedious and really annoying, can’t I just block a certain IP address from posting a comment or even viewing the site?

Can anyone tell me how this is done?

Thanks in advance!