This is not a criticism, just noting a fact. Chasing a fish with a net is the most severe stress you can cause the fish (this is why so many newly acquired fish develop ich). It is the "escape predator" response which I will explain (the physiological aspects) after I describe the easiest way to catch fish to reduce this as much as possible.
Use a larger (rather than smaller) net, stationary against the front glass and near the left corner (if you are right-handed, left-handed may find it easier on the opposite corner). Use your other hand to slowly move the fish to the left side and then toward the front. Usually they will swim right into the stationary net (make sure it is fully extended in the water so they can actually swim into a "cave" of sorts). Using a black net is said to also help, as it cannot bee seen unless you move it; don't know if this is 100% true, but after I got a black net the task was easier.
Here is an explanation of how this seriously impacts the fish; taken verbatim from The Manual of Fish Health.
The most basic stress response is to escape from imposed danger, which may take the form of a natural predator or, in captivity, the fishkeeper attempting to catch the fish in a net. The first part of this response is the preparation of the body for escape, which, in biological terms, involves the release of hormones that channel all the fish's energy to power locomotory muscles. Unfortunately, this alarm response has long-term detrimental effects. For example, one of the hormones released is adrenalin, which apart from "quickening" the body for instant action also disturbs the osmoregulation (i.e., control of the salt/water balance) within the fish. Another hormone involved, cortisol, affects the white blood cells and reduces their effectiveness in the immune system. The second part of the response involves the recovery of the fish's equilibrium. Thus, the alarm response is clearly a compromise between the short-term need to reach immediate safety and the longer-term side effects of the physiological changes involved. It can be an uneven compromise; a fish that undergoes an alarm response as a result of stress applied for even a short period of time can take hours or even days to recover the equilibrium. [Note, "equilibrium" means the condition in which all acting biological (internal) influences are balanced or canceled by equal opposing forces, resulting in a stable system.]