on @*:TEXT:!ban &:#clanbase.crew: {
if ($3 = %null) notice $nick !ban nick chan - chan is either #clanbase or #clanbase.help

else if ($2 !ison $3) notice $nick $2 not found on $3 $+.

else if ($2 ison #clanbase.crew) notice $nick $2 is crew, nice try.

else {

ban -u50 $3 $2 3
kick $3 $2 Punisher says: ROAR!@#

notice $nick $2 kicked from $3 $+.

}

}

-----

[13:10] <Bleah> !ban crap
[13:10] -[CB]Punisher- !ban nick chan - chan is either #clanbase or #clanbase.help
[13:10] <Bleah> !ban crap #clanbase

Where did I go wrong?

on @*:TEXT:!ban *:#clanbase.crew: {
if ($3 == $null) notice $nick !ban nick chan - chan is either #clanbase or #clanbase.help
elseif ($2 !ison $3) notice $nick $2 not found on $3 $+.
elseif ($2 ison #clanbase.crew) notice $nick $2 is crew, nice try.
else {
ban -ku50 $3 $2 3 Punisher says: ROAR!@#
notice $nick $2 kicked from $3 $+.
}
}

Well on what you pasted i could only see some small things. For example, it should be $null and not %null. secondly,the correct syntax is == and not = (although both would work).
I also combined the last kick/ban command... this should work

The problem is simply your match text. & matches any one word. Not two or more.

Thanks!