Tags whose first real revision was a suggested edit will have a blank first revision, attributed to Community, that you can roll back to without any fuss. For tags whose first revision was submitted as a binding edit by a user with 20k+ reputation, though, that's not an option, so you need a bit of a more convoluted method. This will remove both the main tag wiki and the usage guidance (excerpt), though; if you want to preserve one of them, you'll need to either save the text somewhere or find it later at /admin/orphan-wikis.

This has been tested and proven to work. There are three main steps:

First, create a new tag with a blank excerpt. It does have to be added to a question for this to work. So, for example, create a new tag [tag:tag-wiki-fix] on a question.

Secondly, merge the tag with the plagiarized wiki into the new tag. If [tag:william-shakespeare] has the plagiarized wiki, merge [tag:william-shakespeare] into [tag:tag-wiki-fix].

This can be done from /admin/merge-tags. Set the tag with the wiki you want to remove (i.e., [tag:william-shakespeare] as the "source tag") and the new tag you just created ([tag:tag-wiki-fix]) as the "target tag".

[![Screenshot of the merge tags tool, showing william-shakespeare as the source tag and tag-wiki-fix as the target.](https://i.sstatic.net/6arlH.png)](https://i.sstatic.net/6arlH.png)

Thirdly, merge them back the other way - rename [tag:tag-wiki-fix] to [tag:william-shakespeare]. As with a normal tag rename, you don't need to actually add the properly named tag to a question for this step.

These steps will orphan the tag wiki that was originally at [tag:william-shakespeare], leaving you with a blank wiki. The removed tag wiki and excerpt can then be found at /admin/orphan-wikis (unless that page happens to be broken or overloaded).