We all know circlers, players that will run in circles to avoid being hit by an alien while being able to chaingun the poor creature till they die. Here is how to defeat this noobish technique. The human will start running in one direction, usually counterclockwise. Instead of chasing them around this way, you must turn and face the other way, but do it quickly so they do not notice. They will continue running, and run right into you, where you can eat them!
Another trick is to get in the center of the circle, then just slash them in place, turning your view, but not moving.