If you manage many authors and you don't want to allow them to choose more than one category for each post, you need the right plugin. There are benefits to ensuring categories are limited to just one per post. Here's how you make this possible.
<h2>Using the Category Metabox Enhanced Plugin</h2>
By using the <a href="https://wordpress.org/plugins/categories-metabox-enhanced/">Categories Metabox Enhanced WordPress Plugin</a>, you can actually eliminate the possibility of authors selecting more than one category. Start by downloading the plugin and installing it within your WordPress Dashboard. Once you've installed and activated the plugin, you will find the options for it under "<strong>Settings&gt;&gt;Categories Metabox Enhanced</strong>" in your dashboard.

<img class="alignnone size-full wp-image-7286" src="https://itxdesign.com/wp-content/uploads/2014/10/CategoriesMetaboxMenu1.png" alt="Categories Metabox Menu" width="165" height="296" />

&nbsp;

Within the plugin settings menu, you will be able to make all the necessary changes. Under Option Type, you have three options, which include checkbox, radio and select. If you choose the checkbox option, you can still select multiple categories for each post. The radio and the select option will take this option away.

<img class="alignnone size-full wp-image-7287" src="https://itxdesign.com/wp-content/uploads/2014/10/OptionType.png" alt="Option Type" width="575" height="135" />

Choosing the radio option is the best way to keep authors from choosing multiple categories for posts. However, if you have a large number of categories, the select option will give you a dropdown box for your categories instead.

You can also change the position and the priority of the category menu in the post edit screen.

<img class="alignnone size-full wp-image-7288" src="https://itxdesign.com/wp-content/uploads/2014/10/PriorityPosition.png" alt="Priority Position" width="420" height="265" />

This plugin will also allow you to change the title of your categories metabox. You can also disable the indent for any child categories and even restrict users from creating any new categories with this plugin.

<img class="alignnone size-full wp-image-7289" src="https://itxdesign.com/wp-content/uploads/2014/10/TitleIndent.png" alt="Title Indent" width="657" height="273" />

Once you have selected all the necessary options, just save your changes and your categories will have changed in the post edit screen. Using this plugin makes it easy to make sure each blog post is only assigned to one category, which is highly recommended.