I suspect after a few percent get kicked out the other folks would improve their behaviour.

Fair enough. In that case, stipulate that "Heated banter should be expected. If you can't handle that blah blah." Basically, there's better solutions than the shotgun approach.

Are women incapable of understanding that people can be a-holes especially in an unregulated "sporting" competition? Lots of a-holes out there. Just put a warning, let women know, and offer advice if necessary. This is just plain ol' wrong.

It's EA so I'm already boycotting it. :P

I think they are fully capable of understanding. But I can guess that the LAN party probably gets tons of complaints regarding assholes and women every year and just decided to put a stop to it.

Just look at a site like Reddit (which probably is the same demographic as a LAN party). As soon as a women appears, the assholes come out.

Then it probably should not be held.

What kind of person even wants to host an event for a bunch of immature teenage gamers who can't handle the presence of a female?

The problem is that many gamers fall into this category.

Which is a problem to be fixed, not a quirk to be tolerated.

Expect decent behaviour, and expel those who cross the line. Teenagers are fully capable of learning to behave in public.

Exactly, stop catering to the (apparent) animals.