stay in the pocket

1. To remain rhythmically complementary to other musicians or to the song itself. Don't go off on some weird, experimental solo, Tom. This is an ensemble piece, so stay in the pocket.

2. In fighting sports, especially boxing and mixed martial arts, to remain within striking distance of one's opponent. He's got a devastating punch, so try not to stay in the pocket for too long at any given time. She wants to dance around the ring to tire you out, but you're going to stay in the pocket and keep the pressure on her.