Our system has experienced a new force, which sent it out of equilibrium- a fish biting the lure. So what happened to the forces in our system? How were things changed?

Let's start with the lure end of the system. A force was applied to the lure in the opposite direction of motion, increasing the tension. This tension then exceed the maximum force of the clip holding the line. At this point, a number of phenomenon happen: The tension in the fishing line goes to nearly zero, the length of the line shortens because of its elastic nature, the rod tip returns to its equilibrium position, and the downrigger becomes separated into its own system.

At this point, any smart fisherman would reel the slack out of the line. This process was started due to the potential energy in the rod and fishing line. The downrigger can now be cranked up, and the fight with the fish begins. Physics continues to rule the system long after this point.