This should be how it's solved:
ROUND 1:
1. Declaration Phase: each combatant declares his actions. This includes the OB/DB split (parry)! So each character should state who's going to attack and how much OB will he put into defending himself.
For example:
- Fighter (Total unmodified with his weapon OB 100): I use 100% of my activity to attack the orc with 70 points of my OB and parry with the other 30 points.
- Orca (Total unmodified with his weapon OB 100): I use 100% of my activity to attack the fighter with 90 points of my OB and parry with 10.
2. Roll Initiative
- The fighter goes first
3. Resolve short actions (actions that use less than 50% of activity)
- In this example there are no short actions, so this part is skipped
4. Resolve long actions
- Figher rolls his attack, add 70 (OB he used to attack) and subtract Orc DB (plus 10 points, since the orc parried with 10 points of his OB).
- 12 hit point and a B puncture critical. The crit says: 5 HP and -10 to all actions due to broken bone.
- The orc lower his current HPs by a total of 17 (12+5) and, from now on
until he's cured he will suffer a -10 penalty to all his actions due to a broken bone.
- Now the orc attacks, rolling a d100 and adding 90 (OB he used to attack), subtracting fighters DB (plus 30 points, since the fighter parried with 30 points of his OB) and 10 other points because of his penalty.
Basically, i don?t know if in a given combat round one combatant is attacking and other is defending, and in the next one the attacker will be the defender and vice versa or if all combatants will be able to performs attacks and defends in a single round.
During a round each combatant will have a chance to act, attack and defense are part of the same roll (the attack roll) and are represented by the amount of OB used to parry and/or attack. The more OB you're using to parry the more you're fighting in a defensive way, but this doesn't prevent you from making an attack roll! Even if you use all your OB to defend yourself, you may still attack, with an OB of zero.
Edit: and welcome to the forums!