I just learned this game this past week from my fellow music teacher Dee Dee and I love it! It can be used in so many different ways!
Music tag works just like real tag in that there is an IT trying to catch other people. However, in music tag ALL are singing and can only move on a certain part of the song- whatever concept you may be working on. Today we played with Long short (or dotted quarter eighth note) and the students could only step when this rhythm came up in the song. I have also played where students sing and only move on the LAs in a song. The kids love it.
I do it so that if you get tagged you become the new IT- and if you move at the wrong time you are OUT. You could also do, if you get tagged, it is your job to play the element on an instrument. I have heard of only moving on the strong beat, only on the half notes, only on the do's, etc. Just make sure the song you choose has enough of the element to make it fun. If there is only one in a four phrase song, students are standing much more than they are playing tag.