How can I recover from a frozen fullscreen application / game?
Search for the Starcraft 2 process in the process list. I don't know the name of the binary but something like ps aux | grep -i starcraft should get you there
The number in the second column is the PID
kill PID or (if this doesn't work) kill -9 PID (if you are not the owner of the process, you can use sudo kill ... instead)


Depending on the process structure of Starcraft 2 you may need to do this several times to hit the right one.