The band were playing in the stage.
The band played on the stage for the charity event.
A band could play on stage for many things other than a charity event.
exists e1 x1 x2.(n_stage(x2) & n_band(x1) & in(e1,x2) & Actor(e1,x1) & v_play(e1))
exists e1 x1 x2 x3 x4.(n_event(x3) & of(x3,x4) & n_charity(x4) & n_stage(x2) & n_band(x1) & for(e1,x3) & on(e1,x2) & Actor(e1,x1) & v_play(e1))