With a tie-down, you simply attach your dragline to a fixed object like a fence, stair rail or another immovable object like an eye-bolt in the wall. This exercise uses the same principles as teaching the “wait” command, only instead of closing a door or gate, the pup is confined by the leash. That keeps you safe from mouthing and claws and prevents the pup from jumping up and grabbing. Practice puppy sits and downs while you stay out of range. Only reward the puppy with contact from you when he stays calm with all four feet on the floor.
If a dog is stressed or afraid, their demeanor and typical behaviors will change. If you see this in your dog (or really any dog you know) you should step back and check on your dog. Are they hurt? Did a new dog come around they don’t know? Has the weather changed? Is it hot outside? When was the last time they had a chance to go outside to pee or poop?
When a dog jumps on a human of its own free will, it is not "greeting" the human, it is asserting its dominance over the human; it is the dog communicating that it is alpha and/or wishes to own/control the human. A subordinate would never dream of running over and jumping on the alpha dog of the pack. Space is respect and lower members of the pack respect the higher members. If your dog jumps on humans, it does not respect them. Note: when a young puppy jumps on humans it is sometimes its attempt to reach one's face. Puppies need to be taught not to jump up on humans as this behavior will manifest into other meanings as the puppy grows up into an adult dog.