You don't reel in or pull in a BIG fish. You play it. The idea is to get it tired, but not to the point that it's so exhausted that it goes belly up (dies). You do this by throwing it off balance. You throw it off balance by moving it's head so that it's always fighting against the current to regain it's balance. For instance, if it swims behind a rock, you tug on the line to get it's head back out into the main current where it'll need to fight that current to find another quiet slot or eddy.
Also when you have your rod pointed straight up, it acts like a giant spring, and will give the fish little resistance or feel. When you bring the rod down then the spring action gives way to a more direct connection with the line.
So when the fish is somewhat settled down into a hole or a pocket or whatever, you bring down your rod, tug on the line to throw it off balance. As it fights back you lift the rod up so that it acts as a spring. You've got to be very careful that you time everything by feel, if you don't the fish can break off easily if it catches you with your rod held down and pointed directly at it.
As you get good at riding the bull, you'll find all sorts of rod positions that basically do what I've described above.