This page in a nutshell: Wikipedia's Main Pagefeatured article should as a rule not be fully protected, but it may be semi-protected for part or all of the day should vandalism warrant it.
Wikipedia's Main Pagefeatured article is one of the most visible and heavily edited on the site. For this reason, it receives a lot of vandal edits from unregistered users visiting Wikipedia. Consequently, it is and has been suggested many times that the featured article should be semi-protected. Full protection of the page is generally prohibited. Administrators may semi-protect the page for part or all of the day as if the page were any other article.[1] The length of protection is as short as the situation reasonably permits. Possible circumstances under which an administrator might consider semi-protection appropriate are given below.