Remove website url text field from comments form
Removing the website URL field from your comments form may help reduce spam comments. The URL field is normally used by WordPress to collect users’ URLs so as to link them to their names or user names when placing comments. However, spam bots use this field to post worthless comments to get backlinks and traffic from blogs which have this field enabled.
So if you are looking into reducing unwanted comments you may consider using the following code snippet. The snippet applies a filter to the function that generates the comments form. Before rendering the form it strips out the URL text field from the source code.
To use the snippet, just drop it as it is at the end of your functions.php file.