When someone puts someone through something, that person will often feel a certain amount of anger towards the person who put them through adversity. Cops are no exception, and they will always feel a certain way when a person leads them through extra hoops or a tiring chase. When the predator catches the prey, the predator will have the biological impulse to put a beating into the prey.
So when a cop catches someone who made them all tired and sweaty by chasing them, they would naturally have the urge to put the hurting on that person, though it must be suppressed because they are not above the law. They do not always suppress this urge, and thus we have the incidences of police brutality.