Your requested aggressor definition already exists. Your request about pursuit/following/whatever is not something that I believe that could be constructed under our Constitutional freedoms because it would involve restricting the freedom of an individual not committing a criminal act because someone else just didn't like the way he looked. The 5th amendment rather gets in the way of your desire to compel defendant testimony.

Relating back to the Zimmerman case:
Zimmerman didn't physically testify because the prosecution's introduction of the police records already put his story before the jury, and the Defense had no problems with his statements. All he could do was potentially screw it up by saying something to offend the jury (like calling the prosecutor retarded for example), especially with the police officers stating that they found his statements believable.

You keep insisting that Zimmerman accosted Martin, tried to detain him, or in some way physically attacked him. You keep ignoring that there is no objective evidence of this occurring; only biased testimony both ways, the only physical evidence regarding the origins, and continuation, of the confrontation make the theory of Zimmerman as aggressor unlikely.

IF Zimmerman had attempted to do so, he would have committed a criminal act (unlawful detainment, a cousin to kidnapping). This action would have enabled Martin to respond with violence (776.051.2 &/or 776.012). HOWEVER, even under this scenario, Zimmerman would still have a potential self-defense claim if Martin's violence exceeded reasonable levels (776.041.2a). All of this has been covered repeatedly.