For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:tuxtuxtuxtuxtux/openSUSE_Tumbleweed/home:tuxtuxtuxtuxtux.repo
zypper refresh
zypper install assaultcube
For Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:tuxtuxtuxtuxtux/Slowroll/home:tuxtuxtuxtuxtux.repo
zypper refresh
zypper install assaultcube
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:tuxtuxtuxtuxtux/15.5/home:tuxtuxtuxtuxtux.repo
zypper refresh
zypper install assaultcube