Hi dgridley, Youtube videos is of course mandatory

and a forum where girls can discuss and talk about their experiences and progression in martial arts/boxing, wrestling ,etc is also a must do to create a community and make the site sticky so to speak.
Make sure it's a Vbulletin forum since all other forums just put me of in it's design but that's just a personal opinion

But a forum is a must do in my opinion.
A categorized -view video- section with videos from street brawls to wrestling matches is a great way to create stickyness plus you could ad some Google video ads between them
http://adsense.blogspot.com/2006/05/video-ads-your-questions-answered_26.html
but i am not sure how this exactly works if there are no relevant ads to be found for the keywords in your content.
I think only major advertisers are into video ads and the smaller ones selling ebooks and stuff about martial arts and self defense are not as much involved with this type of advertising.
So don't know how effective this can be but i had to mention this.
Adsense is of course one way and the fist plan of "attack" but you could also ad some affiliate links to books about martial arts and self defense.
A "Featured Book" that is being displayed every day on a random basis containing a affiliate link to Amazon or Barnes and Noble that could yield some revenue, i don't think it's that much but it's an extra revenue maker anyway.
Look into selling martial arts gear and sports clothing on the site directly or via affilaite programs or look into the possibilities to approach these type of vendors and ask to see if they are interested in paid advertising on the site?
As you said already, your own shirts containing the GirlFights.info Logo (One for the to-do list: Look into creating a kick ass logo) which you can sell through your site.
Make multiple choices for choosing a shirt design, i.e. for Karate, Kick Boxing and so on.
Here is a excellent
option for you to use (Haven't tried it myself but looks interesting though) to sell shirts and you can use your own designs as well.
Definitely looking into

Since it's doesn't cost you a thing to put up shop. The only effort goes into creating your own original designs.
Personally i wouldn't go for the blog approach but more for a site.
You could integrate a news section reporting primarely about sports women that are into martial arts/fighting sports to create some more stickynes.
Just some thoughts
P.S. The SEO factor is also attractive since the competition isn't that fierce if you look at the numbers for "girl fights"