Old Fox had once tried to trap Gao Yang in a cave, but with the appearance of the Chieftain and his people, Gao Yang managed to come out.
Gao Yang had also attempted to confine Old Fox inside a house and prevent his escape, but with someone sacrificing themselves to divert his attention, he failed, and Old Fox ultimately escaped the cage.
Gao Yang actually did not mind letting Old Fox go; their encounter was coincidental, with no deep-seated hatred. They had to fight upon meeting on the battlefield, but there was no direct conflict initially. Since there was no loss on his part, Gao Yang would not obsess over a mercenary who was only working for money.
But the problem now was that Gao Yang had nearly wiped out all the people around Old Fox. He didn't mind letting Old Fox go, but Old Fox would certainly not let him off. Now, one of them had to die to end this.