Philly Subway Killing: Self-Defense, Accident, or Manslaughter?

Two men, one much larger than the other, get into a physical confrontation on a Philadelphia subway platform, with the larger man holding the smaller against a support column. Suddenly the smaller man--now identified as Chaz Wearing--throws a punch, then another, sending the larger man staggering off the platform and onto the tracks--seconds before subway car enters the station and runs over the fallen man with fatal results. Was this death lawful self-defense on the part of Wearing? Wa...