I know somebody who studies Japanese swordsplay. It's mostly who gets to swing at the other guy accurately first. There's quite a bit of manuevering beforehand, though.

There's an archaeological find on Japanese battlefields that found a lot of soldiers died while having their own sword stuck on their heads and helmets. Apparently, they tried to block their opponents' sword with their own but the momentum of their opponents' sword made their own sword hit their head, killing them. Simple physics shows why this will be the case.

I don't think you can really block a sword with another sword effectively. That's what a shield is for.