Romo stepped forward in the pocket and escaped pressure to his left while Avril closed from Romo’s backside. Romo began to slide as Avril chased him down and was caught in an awkward position as the two players went to the ground.
Romo immediately reached for his lower back area and was tended to be the Cowboys’ training staff being walking off the field under his own power.
Romo was reportedly asking to go back in the game, so this is probably nothing serious. But it's a reminder of Romo's fragility in recent years.