There is something more interesting out there.
Curiosity can make your dog zig zag in front of you. You see when you are outside the house, there are so many interesting things that will be competing for his attention. Maybe it is the smell of another dog that was friendly the last time or that leftover food he has been perceiving all day and now has an actual chance of sniffing out or even tasting properly. Maybe it’s that kid that always gives him that special treat that he looks forward to every day.
Whatever it is, it surely has more attraction than you do and would make your dog to run zig zag in front of you.
Using too much leash
The amount of leash you use can decide how your dog behaves when you are outdoors with him or her. Having a long leash gives your dog the impression that they can move around in front of you exploring everything possible, hence blocking you and moving in a zig-zag motion in front of you.
On the flip side having a short leash or a retractable leash will give your dog the impression that pulling on them is acceptable behavior.
In both cases, your dogs will still end up blocking your way.
Lack of Training
You may be walking zig zag in front of you and tripping you simply because you have not taught it how to behave when you guys go for a walk outside the house. It is just common sense that if you don’t show your dog what you expect from him or her outside the house, your dog will probably feel that they are in the right doing whatever they are doing.
Among all the points mentioned, training your dog ranks high in importance as it can have a positive or negative effect on all the points mentioned.