Is too easy!
A guy in combat mode cant move as fast as one in regular mode. Even if they have similar speed attacker still has to switch to combat mode to strike and that's when runner gets speed advantage. As long as runner has enough health he can get enough distance to retreat safely. Because of that switching to regular mode for repositioning is used too often in combat.
I suggest implementing at least one feature from below or something similar to make combat feel more fluid and natural:
1) If you take damage then you should be automatically put into a combat stance.
2) If you take damage while in combat stance you can't leave it for at least X seconds.
3) If you take damage while in regular stance you are slowed down by X % for X seconds.
The main idea is to make combatants commit themselves to the process. If you are in a fight you should fight, not pace back and forth sheathing and unsheathing a weapon. The only way out should be usage of the "Flee" ability and it should have a cooldown of at least 10 minutes or more.