I think is is important to play to the tempo of the game. If it is a large complex battle for example lots of goblins and one flees i have no problem with the pc sucker punching a gobo with maximum bonuses, just for the sake of speeding up the game, if the foe is fleeing hes already defeated. So everyone is happy. But if the foe is a combat hardened or experienced fighter, i would typically have them tactically withdraw. Snap action parry or attack at -20 while retreating backwards at jog x3 pace no additional bonuses to attack with, this also increases the survivability of the pcs if required. And makes following a retreating foe a potentially dangerous situation, if the EXP hungery PC is prepared to move out of position endangering the rest of the party for personal advantage...
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