The Jim Johnson 43 Defense relies primarily on zone reads, with Zone Blitzes executed by the Front Seven, as well as Zone Coverage in the Secondary, in order to make up for the deficiencies of the group, or to roll coverage onto a studly WR or TE. It all starts up front, with the lanes opened up by the DLine, creating gaps for the LB's to blitz through, creating pressure which forces the QB to chuck an inaccurate ball unto which the Secondary makes a play, hopefully forcing a turnover. The different units of the Defense must work in unison, or else the effectiveness of each unit will become moot. For example, if the Defensive Line is being blown off of the LOS, and can't do their job, it prohibits the blitzing LB's from completing their own tasks, allowing an opposing QB/RB to gash the defense as a whole. Furthermore, having subpar players executing a zone will create a weak link in the zone, or an open target for the opposing offense.
The Jim Johnson Defense can be very effective, dialing up pressure from seemingly nowhere, as well as coercing a QB into phantom blitzes that can confuse the opposition. An effective Jim Johnson 43 Defense can keep an opposing offensive coordinator guessing all day, playing into the hands of an amalgamate defensive unit.
http://www.catscratchreader.com/2012/2/28/2831884/the-panthers-defense-a-treatise-on-the-jim-johnson-4-3-part-i
Nice little write up.