He made several tactical mistakes that should never be made.
1) He went up against a crowd by himself without backup. Who would be stupid enough to go up against a pack of feral dogs by himself? Don’t do this.
2) He did not keep situational awareness with an eye to defense. You never let a threat get behind you. A fatal mistake.
3) The first bullets to to the enemy that are armed. In this case, the one with the lead pipe, had he seen him.
4) Even with a group, imagine trying to rush someone with a knife whose back is against a wall, or preferably in a doorway. Not easy. And with a knife and a gun, very not easy.
He made one big strategic error — he should have stayed away from areas where he could encounter large groups of AAs, such as H’burg itself.