You'll notice that on Live-Timing there's a place to enter 'User Name and 'Password'. The next releases of the software will include 'User Name' for added security. To modify a race created without a it, simply leave user name blank.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .