"--track" in linkgit:git-branch[1] for details.
+
If no '-b' option is given, the name of the new branch will be
-derived from the remote-tracking branch. If "remotes/" or "refs/remotes/"
-is prefixed it is stripped away, and then the part up to the
-next slash (which would be the nickname of the remote) is removed.
+derived from the remote-tracking branch, by looking at the local part of
+the refspec configured for the corresponding remote, and then stripping
+the initial part up to the "*".
This would tell us to use "hack" as the local branch when branching
off of "origin/hack" (or "remotes/origin/hack", or even
"refs/remotes/origin/hack"). If the given name has no slash, or the above