I'm assuming you mean
games/rottdc, no other rott port exists.. so after installing it.. you should have seen these instructions.
http://www.freebsd.org/cgi/cvsweb.cg...e=text%2Fplain
According to this file, the game "data files" must be in the current directory.. so if you've extracted the files into your home directory, you must run it from within that directory.
Hope that helps..
EDIT: The "rottdc" port is not the same as the project you've mentioned above.. if you've compiled that manually, you'll have to read their document for further instructions.