catching them in recovery from their first step. 
HIA-
A Hand Immobilization Attack is a way to force an opening through a tight defense.  HIAs, also known as trapping hands, may also be a way of tying up the opponent's weapons so they cannot be used against you.  The origin of trapping in JKD is from Wing Chun Gung Fu, the style Bruce practiced when he was young. 
Examples of HIA:
1) Lead with a low punch to the stomach, When they block, slap their forearm (Pak Sao) with you're rear hand, preventing it from moving while you take advantage of the opening, hitting with a backfist to the head.     
2) While fighting inside, you throw a hook to the head.  If they block the hook, as soon as contact is felt, hook their forearm and jerk (Jut Sao) the arm downwards (Like pulling the lever on a slot machine).  Immediately spring off their arm with the same hand and strike to their head. 
       Trapping can get very complicated.  For effective HIAs, it is best to stick to simple traps, steering away from those that involve several movements. 
     The Five Ways of Attack outline five distinct strategies that can be helpful to any martial artist regardless of experience or style.  Each strategy works together as well as on it's own.  After practicing them individually, you will begin to realize that all are inter- related.  An HIA can also be a PIA, ABCs are made up of a series of SDAs, or you may use an ABD to pull off a PIA.  I know it looks confusing using all those acronyms.  Attacking can be quite simple having the Five Ways of Attack to label your options.