`play run` is sort of the equivalent of `runserver`. `play start` is one of the recommended[0] ways of running Play applications in production.
[0] http://www.playframework.com/documentation/2.1.0/Production
[0] http://www.playframework.com/documentation/2.1.0/Production
http://www.playframework.com/documentation/2.1.0/ProductionD...
So without the framework installed and in your PATH, you can just go to an app's directory and do "sbt start". It will download all dependencies needed, compile your app and start the server.