AdiIRC

The ban must always be on an address mask, so you would need to create a wildcard which matches what you want to do.
$address(nick,mask number) can create different masks, but only if the nick is in the internal address list
//echo -a $address($me,3) is one example.
If your input is someone's full address, you can use $mask(string,mask number) to translate it to one of the various address types
//var %address nick!~userid@subdomain.isp.com | echo -a $mask(%address,3)

You weren't clear what kind of host ban you wanted, that specific hostname, or their entire ISP, etc?
There's not a mask number for each type, so sometimes you need to create the ban mask yourself
To match a specific nick regardless of address:
//mode #channel +b $+($nick,!*@*)
To match userid regardless of hostname:
//var %address nick!~userid@subdomain.isp.com | echo -a $gettok($gettok(%address,2,33),1,64)