The National Football League is very protective of its NFL trademark. Best not to take the chance unless your site has nothing to do with football and NFL stands for something else.
Take note of tobycoke's answer. You actually can, but your usage is limited and it might invite unwanted trouble.
The trademak is for the country where is registred the trademark for example if you register nflcoolboy dot com, and you will make business in India, and in India there is not a NFL related trademark registred, you will have not problem, but if you are going to created something for USA, you will have problems... Best
thanx for the response guys! im gonna take another route, and think of another name. I had a domain name with "ipod" in it, i just deleted it because someone said that its not safe having the word "ipod" in your domain name. Kinda sucks i had to delete it, i was getting 100+ uniques a day, with no advertising, just adding it on google and yahoo. Oh well..
I Don't tjhin kyou wanna buy a domain with NFL in it. Rich jerk was gonan sue someone for having a domain with richjerk on the domain lol
One of my clients site I was working on had NFL in the URL and the sued him and took the site. I would NOT RECOMMEND doing it I never saw him again or my money, even though I did the work