Some times people kill sharks for sport while fishing.
Other times, humans kill sharks for fishing to use their meat as food and to use their fins for medicinal purposes.

This practice is extreme and very cruel. When a shark is captured by fishermen, the shark is plucked from the ocean and every fin on its body is cut away. Do you know what is next? The sharks body is cast back into the sea alive. What happens is that without fins a sharks body drifts to the bottom of the ocean and the shark starves to death. Without fins a shark cannot stabilize its own body in the water to continue to swim. A shark needs to constantly swim to survive in the environment so that the sea water constantly stimulates its gills. Water flows over the gills as the shark swims. The shark is left alive when cast over the boat back into the sea. Did know that? That my friend is horrific. Just think, what if the same was done to humans for arm and leg soup. What if fishermen caught us cutting off our legs and arms for the same purpose and leaving us to starve and die. The most humane thing to do here is to use the entire body of the shark and kill it so that it doesn't suffer so horribly, don't you think? Sharks also need meat for food too. The medicinal part I could care less about. Sharks have as much right exist in this world too and have been around on this a lot longer than humans. We all need to respect that.