Annotation of content is a key enabling technology for multimedia systems development. In this demonstration, we present a real-time activity annotation interface designed to be intuitive while imposing minimum effort on the user. Our solution is to use a smartphone and implement a tile-based touch interface. The interface was developed as a part of a larger project in collaboration with Tromsø IL, one of the top soccer teams in Norway. In this demonstration submission we present and evaluate the annotation interface of Muithu. © 2014 Springer International Publishing.