Defensive pistol shooting as a sport is quite simply the use of practical equipment including full charge service ammunition to solve simulated "real world" self-defense scenarios. Shooters competing in Defensive Pistol events are required to use practical handguns and holsters that are truly suitable for self-defense use. No "competition only" equipment is permitted in Defensive Pistol matches since the main goal is to test the skill and ability of an individual, not his or her equipment or gamesmanship.
For more info see http://www.idpa.com