Player B runs away, and jumps to System B.
Player B repairs.
PLayer A jumped to System B.
Player B engages Player B in System B.
As far as I know it's allowed by the rules.
Quote:5.8 A player who was killed in a PvP fight must not re-engage the enemy (player or players involved in the death) with any of the characters on his/her account(s) for 4 hours.
But Player B never died, so this rule doesn't apply.
Quote:5.6 If a player engages cruise engine or docks during a PvP fight, this player is considered fleeing. The fleeing player must leave and may not re-enter the system where the fight took place with any of the characters on his/her account(s) while the enemy (player or players involved in the fight) remains in the system, but no more than 4 hours.
As long as Player B doesn't enter System A while Player A is in it, there is no breach of rules.