in Jun Fan JKD, we use five different ways to get in...
The Simple Attack (SA) - This is, simply, hitting or kicking the opponent at the precise moment of an opening. It is a difficult aspect to master as it requires mastery of timing, range and speed. The majority of attacks used in boxing are simple attacks. Bruce felt that this was the most advanced way to attack someone which led him to the concept "offense is the best defense." In Chinese, there is a saying, "you start first, but i get there first."
Attack by Combination (ABC)- this is using two or more percussive attacks in combination to elicit a specific response from the opponent, creating an opening so the final blow or blows land unobstructed. Also seen in boxing, the classic example is the one-two, which is a jab to the chin and then a cross to the jaw. The jab raises the chin to expose the jaw, which causes a knockout if hit right. Some of the best ABC combo's are done by shifting levels; high, low, high or low, high, low.
Hand Immobilization Attack (HIA) This describes the trapping and grappling ranges of fighting, Where the fighters are attached to each other either by the work of one or both fighters. In Boxing, this is known as the clinch, where you close distance with the opponent and work to 'hug' him so he can't punch you. In streetfighting, as Bruce points out, you can do things like headlocks and hair pulls as well. So it's important to remember that they are a part of HIA. HIA can also include the feet or legs. Generally HIA is used to control the opponent and to transition to other attacks.
Attack By Drawing (ABD) This is when you let your guard down on purpose (giving your opponent a false opening) to get the opponent to attack a specific area which you'll be ready for with a counterattack.
Progressive Indirect Attack (PIA) This is to move in to attack, faking your angle of attack on the approach to elicit a defensive response from the opponent, then changing the angle to the real angle of attack thus scoring a hit. In a nutshell, fake low, hit high or fake high and hit low.