When a frigate's last escort gets destroyed, a new group of escorts immediately gates in and heads for the frigate. If a friendly station is located close to a stargate and between the gate and the frigate, you can get a situation where pirates are gating in and getting destroyed pretty much continuously. This can also happen if the player is fighting a frigate near a stargate. A 15- or 20-second delay between the destruction of the last escort and the arrival of the next group of escorts would alleviate this.