A quick block for clients that bother you somehow or do malicious stuff.
sudo fail2ban-client status
Choose the jail you want to block the IP from/add it to.
sudo fail2ban-client -vvv set [JAILNAME] banip [IP]
Replace [JAILNAME]
with a jail from first list and [IP]
with the IP address to be blocked.
The block is not permanent and will be removed on reboot/restart of fail2ban.