Our society is mostly a leashed one, leash laws are in place everywhere. They are there for a reason and are often enforced. So as we walk our dogs through the streets, parks and beaches we come across others with their dogs on leash. We may or may not greet depending on the look of the other dog, our own dogs reaction to other dogs on leash or if we want to stop and say hi. If we do it can be all undone in a moment, that friendly greeting can go bad quickly and not because of either of the dogs being grouchy. If you are not careful with your leash the two dogs can become entwined quickly.
Yesterday I had Elsa at the park for a walk, we ran into a guy with a nice Weimaraner. I am trying to teach Elsa that we can simply walk past dogs without engaging every time but this looked like a nice girl so we went to say hi. She was very nice and Elsa got very excited. Within a split second Elsa was in a tangled mess. The other dog was on an extension leash and the guy was not controlling where she went at all; he was allowing her to pass that precise point where tangling starts.
Dogs greet by circling, each wants to smell the other dogs parts so of course it's going to result in a circling behavior. If you allow your dog to go past the neck to neck they are going to get tangled. I keep Elsa front and center because I never want to deal with tangling issues. But when you are dealing with other people you cannot control what they do. So his leash quickly got wrapped around Elsa as she bounded around and I grew angry. I grabbed her to stop her from moving an unwrapped the leash from her legs before she got hurt and said "okay that's enough." We moved on.
Allowing dogs to greet on leash can be a challenge at the best of times, many dogs show leash aggression. They feel constrained by the leash and often act very different from their off leash self. But the leash can cause problems all on their own. If a dog becomes wrapped up and feels like they cannot get away they can become defensive causing aggression and a learned behavior. The leash can also get wrapped around them so tightly that they fall to the ground. Tangled leashes are a big danger both physically and mentally. Tangles are to be avoided at all costs.
If you want to say hi to another dog keep your distance, do not cross that invisible tangle line. Once two dogs facing each other cross collars the tangle can begin. If you want your dog to move around the other dog then you need to move with your dog keeping the leash at a short length. If you are one of those folks out there using an extension leash, reign that baby in and lock it when you approach other dogs. They are by far the most dangerous leash out there for tangle accidents. If you approach someone with an extension fully extended, keep walking.