play first chair

1. to be the leader of a section of instruments in an orchestra or a band. (More literal than the following sense.) Sally learned to play the violin so well that she now plays first chair in the orchestra. I'm going to practice my flute so I can play first chair.

2. Fig. to act as a leader. I need to get this job done. Who plays first chair around here? You're not the boss! You don't play first chair.