This subject gets discussed regularly on Sports Photography forums, (such as the sports forums of fredmiranda.com and photography-on-the.net, and the mesage boards of
www.sportshooter.com).
Firstly, the coach cannot copyright the images. As the photographer the copyright remains yours unless you sign an agreement that transfers copyright to another person/organisation. If the coach does not have your permission he cannot use these images. If you are serious about resolving this then contact an attorney who is a specialist in copyright law before you do anthing else.
However the question you need to answer is how far do you want to go to get this sorted. If you were a pro photographer making a living from these images then contacting an attorney would be the obvious choice, but if you are just doing this for fun then you probably do not want to spend time and money so some options may be;
1. If the coach has ignored your request for the removal of the images then contact the club president. He may be keen to resolve this in case you decide to sue and the club gets involved in any litigation.
2. Contact the web hosting company that the coach is using to post the images. Tell them he is using copyrighted images illegally and they may remove them in case they get sued for copyright infringement. Long shot but may work.
3. If you know an attorney who will draft a letter for you then send it to the coach stating that you hold the copyright to these images and if he does not remove them you will sue for damages and attorneys fees.
4. Send the coach an invoice for the use of the images. A search of the web should give you some idea of what a pro photographer would charge for unlimited use of sports images, and just multiply it by the number he has used.
There are a couple of things you can do in the future. Make sure that the team website includes a copyright notice stating that you are the copyright holder and any unauthorised use is prohibited, (and just let the parents know that they are authorised to copy or print them). Also consider including a watermark on each image, as there are programs that can quickly batch process this onto multiple images.
One last tip - if you decide to go further with this and contact an attorney then make sure you copy the original images onto a CD and send it to the US Copyright Office. There is a small fee but this will allow you to collect not only damages but also attorneys fees if it is within three months of the coach first using your images. See
http://www.krages.com/copy1.htm for more details