Squared up while in motion , only time Arbery stopped is when he was violently attacking the hero
Another new fact we learned is that TravisM fired the first shot that hit Arbery in the chest before Arbery started violently attacking your hero.
If the wounded jogger knew anything about a pump action shotgun and being at close range his best self defense could be preventing the whackjob that just shot him from pumping a new shell into the barrel of the shotgun.
Either way there is no way Arbery would not have been entitled to kill the attacker with his own gun if he could get it away from him. specifically entitled to self defense since he was wounded. The wound would give investigators evidence that TM shot Arbery at close range which is where he should not have been - blocking AA’s means of escape.