If you control the copyright, anywhere.
If you don't control the copyright, and don't have a license, nowhere.
I don't think so. It involves copyright issues. You can print something more common on your tshirt, for example, natural scenery. That is to say, you can not put something related to names or personal images on your tshirt.
No, and copyright would be less of a problem than trademark. The NFL is particularly fastidious about protecting its brands.
The author of a creative design is the owner of the copyright automatically.
Fortunately or unfortunately, copyright law isn't as black-and-white as that. If the design is protected by copyright, then only the copyright holder can copy it or authorize others to do so. Some copying is allowed by limitations, defenses, and exceptions in the copyright law itself. And the design may not even be protected in the first place, if the term has expired. So yes, copyright law means I can't put a Picasso on a t-shirt and sell it without a license. But I can take a photo of it or attempt to recreate it in my art class.
Copyright someone elses design
If the design meets the minimum requirements for copyright protection, yes.
If the patterns are under copyright then you need the permission of the copyright holder to sell them.
Aspects of the design that are entirely your original work, such as a piped or carved design, may be protected by copyright as a work of visual art; the US Copyright Office has asserted that permanence is not required for protection.
Do a google image shirt of "tshirt" and find an image of blank tshirt. Then use photshop or illustrator to add pictures/text as a template. You can find iron-on pages at many stores such as WalMart or Target that will feed through your printer and you can iron them onto a tshirt
Animators wear usually a tshirt with a cartoon on it or design with blue jeans. Be creative about it though!
Yes, if the web design legally belongs to you. Add © copyright YEAR NAME OF COPYRIGHT HOLDER to the bottom of each page of the website. This will signal to honest people that the web design is copyrighted and may not be used elsewhere.
If you mean "Can you sell a pattern copyrighted by someone else?" the answer is yes but only with permission. If you mean "Can I create a pattern from scratch, copyright it and sell it?" the answer is yes.