Snowball is part of the revolution against Mr. Jones and, with the other pigs, becomes one of the leaders. Snowball attempts to form committees and educate the animals. Snowball gives rousing speeches and has many grand ideas. Unfortunately, he and Napoleon don't see eye to eye. Their disagreement comes to a head when the animals vote on the windmill. After Snowball's speech, "there was no doubt as to which way the vote would go." However, Orwell tells us that Snowball "often won over the majority by his brilliant speeches, but Napoleon was better at canvassing support for himself in between times." Napoleon has secretly trained dogs that attack Snowball and chase him off the farm.
Snowball's disappearance is the perfect opportunity for him to become a scapegoat. Napoleon and Squealer manipulate the animals by blaming things on Snowball. Squealer is a persuasive speaker, and he becomes Napoleon's mouthpiece. Napoleon "issued his orders through one of the other pigs, usually Squealer."
When the windmill is destroyed, Napoleon blames it on Snowball:
“Comrades,” he said quietly, “do you know who is responsible for this? Do you know the enemy who has come in the night and overthrown our windmill? SNOWBALL!” he suddenly roared in a voice of thunder. “Snowball has done this thing! In sheer malignity, thinking to set back our plans and avenge himself for his ignominious expulsion, this traitor has crept here under cover of night and destroyed our work of nearly a year.
This is "proven" by the footprints found:
Almost immediately the footprints of a pig were discovered in the grass at a little distance from the knoll. They could only be traced for a few yards, but appeared to lead to a hole in the hedge. Napoleon snuffed deeply at them and pronounced them to be Snowball’s. He gave it as his opinion that Snowball had probably come from the direction of Foxwood Farm.
As the leader, Napoleon must deal with the problems that arise, such as the food shortage. In chapter seven Orwell writes, "no more had been seen of Snowball." This is turned around in the very next paragraph:
Suddenly, early in the spring, an alarming thing was discovered. Snowball was secretly frequenting the farm by night! The animals were so disturbed that they could hardly sleep in their stalls. Every night, it was said, he came creeping in under cover of darkness and performed all kinds of mischief. He stole the corn, he upset the milk-pails, he broke the eggs, he trampled the seedbeds, he gnawed the bark off the fruit trees. Whenever anything went wrong it became usual to attribute it to Snowball.
Orwell suggests this is not true and simply something the animals have been manipulated into believing.
When the key of the store-shed was lost, the whole farm was convinced that Snowball had thrown it down the well. Curiously enough, they went on believing this even after the mislaid key was found under a sack of meal.
Napoleon investigates this himself:
With his dogs in attendance he set out and made a careful tour of inspection of the farm buildings, the other animals following at a respectful distance. At every few steps Napoleon stopped and snuffed the ground for traces of Snowball’s footsteps, which, he said, he could detect by the smell. He snuffed in every corner, in the barn, in the cow-shed, in the henhouses, in the vegetable garden, and found traces of Snowball almost everywhere. He would put his snout to the ground, give several deep sniffs, ad exclaim in a terrible voice, “Snowball! He has been here! I can smell him distinctly!”
Throughout the text, Napoleon spreads lies, often with the aid of other pigs like Squealer.
It's Squealer: ever since Snowball was driven from the farm, Napoleon's propagandist-in-chief has never lost the opportunity to trash Snowball's reputation, making him out to be a traitor to the Animalist Revolution. It's Squealer who turns Snowball into a scapegoat for the many problems that have befallen the farm, most of which were due to Napoleon's incompetence.
The collapse of the windmill is a case in point; it was so poorly constructed that it was blown down quite easily in a storm. Napoleon immediately heaps the blame for the windmill's collapse on the absent Snowball. The ever-loyal Squealer sees this as an great opportunity to turn Snowball into a boogie-man figure, someone who can conveniently be blamed for the regime's numerous failings.
With a completely straight face, Squealer accuses Snowball of regularly sneaking back onto the farm in the dead of night and committing acts of sabotage. Apparently, this is because he's formed a treacherous alliance with the hated human oppressors and is determined to do anything he can to undermine the Revolution and make himself ruler of the farm with the help of the enemy's assistance.