Hi,
Sorry for the delay here.
I responded yesterday, but looks like I closed the tab instead of submitting it.
Your are referring to SPAM user registration and not SPAM events correct?
We do not modify the WordPress registration system so we do not having anything to directly support.
However, there is a bunch of plugins that can help.
This plugin might work for you:
Spam protection, Anti-Spam, FireWall by CleanTalk
This search brings up many more as well:
https://wordpress.org/plugins/search.php?q=spam+registration
Let me know if that is what you are looking for.
Cheers