Jeet Kune Do, unlike many other methods, is not a defensive type of combat.  JKD follows an approach explained with an expression used in modern sports; 'The best defense is a good offense.'  JKD favors a hit first and ask questions later approach rather than letting the opposition dictate one's course of action.
From Bruce's research into the art of combat, he concluded that there are ultimately five methods of attack.  These five ways are not meant to exclude any of the infinite number of specific attacks that are possible.  He wrote them aiming to generally categorize all modes of attack. 
The 'Five Ways of Attack' are as follows:
SDA- Single Direct Attack
ABD- Attack By Drawing
ABC- Attack By Combination
PIA-   Progressive Indirect Attack
HIA-   Hand Immobilization Attack
SDA-
An SDA, or
Single Direct Attack, is one single strike, taking a direct path to the target.  Although it is probably one of the most difficult attacks to land, it is definitely the most important to master.  Strong SDAs make strong fighters.  If you were able to land an SDA with successful consistency, you would obviously out class your adversary.  An SDA takes precise timing, distance, and a keen awareness. 
Examples of an SDA:
1.) A straight lead to the head when they drop their guard. 
2.) A front lift kick to the groin area.
3.) A side kick to the open ribcage.
An SDA is a very simple attack, involving no set up or preparation.  It is an attack that takes advantage of holes in an opponent's defense.
ABD-
ABD stands for Attack By Drawing.  It is a set up.  It draws the others into a situation that enables you to strike.  You can draw them to make an attack that you plan to counter.  They can be led a certain direction so that you can intercept or simple get them close enough to hit.  Most ABD type attacks require a level of comfort that can only be achieved through numerous sparring sessions.  It is necessary to be able to think clearly during the confrontation.  ABDs are preplanned; they are a manipulation of you opponent's actions.
Examples of ABD:
1.) To close the gap, you back away.  As they follow, shorten each of your steps gradually so that it goes undetected.  With each step getting shorter, they come into your range without noticing.  As soon as they are in striking distance, attack.
2.) Purposely leaving the right side of your head unguarded, you attempt to draw a jab out of them.  When they throw the jab, you counter with a slip and a strike to the ribcage.  (Distance is important in this.  If you stand out of his punching range, you are likely to get kicked in the head while waiting for the jab)

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