Snowball is used as a scapegoat because he is wrongly blamed for everything that goes wrong or might go wrong on the farm. In chapter 6, for example, the windmill that the animals spend so long building is destroyed by a storm. Napoleon doesn't want to acknowledge that the storm is responsible for the destruction of the windmill or that he didn't direct the animals to build the walls of the windmill thick enough, and so he tells the animals that "Snowball has done this thing!"

Napoleon scapegoats Snowball here because he knows that it is to his advantage to give the other animals a scapegoat to blame their problems on. If there is a scapegoat that Napoleon can villainize, then it allows Napoleon to better present himself as the hero, savior, and protector. Napoleon also knows that if he acknowledges that the storm has destroyed the windmill, then this will probably demoralize the animals. However, if he blames it on Snowball, he can galvanize the animals around their collective dislike of Snowball and make them build the windmill again.

Later in the story, Napoleon spreads the rumor that Snowball sneaks onto the farm in the middle of the night to sabotage the farm. According to Napoleon, Snowball steals the corn, spills the pails of milk, and smashes the eggs. Indeed, whenever anything goes wrong on the farm, it becomes "usual to attribute it to Snowball." By making Snowball a scapegoat for everything that goes wrong on the farm, Napoleon can deflect blame from himself. He is, after all, the self-declared leader of the farm, and so he really is accountable for anything that goes wrong.

Napoleon succeeds in making the animals believe that Snowball is a constant menace and threat to the farm. Eventually the animals become "thoroughly frightened" of Snowball, and imagine him to be "some kind if invisible influence, pervading the air about them and menacing them with all kinds of dangers." As noted above, this successful scapegoating of Snowball allows Napoleon to set himself up as the protector of the animals, and in doing so, it becomes easier in turn for Napoleon to command the loyalty of the animals.

Napoleon heartily detests Snowball. He's much more intelligent and charismatic than he is, and he is a better organizer to boot. While Snowball was personally spearheading the defense of the Animalist revolution during the epic Battle of the Cowshed, Napoleon was missing in action. Snowball's conduct during the Battle showed clearly who was the better leader, and Napoleon hates him for his superior leadership skills.

Realizing the threat that Snowball poses to his power, Napoleon has him chased from the farm. But even after that, Snowball remains Public Enemy Number One. Among other things, this means that his reputation must be systematically trashed.

To hear Squealer tell it, Snowball is personally responsible for everything that goes wrong on the farm. According to him, Snowball's a traitor to the cause of Animalism and has been actively working in cahoots with Mr. Jones to destroy the revolution and restore human control of the farm.

This is all complete nonsense, of course, but Napoleon realizes how handy it is to have a convenient scapegoat on whom he can blame everything that goes wrong. Thanks to Napoleon's shortcomings as a leader, the Animalist revolution is turning sour, with chronic food shortages being the order of the day. But instead of being straight with the other animals and owning up to his inadequacies as a leader, Napoleon puts the blame for all his failings onto Snowball. This way he gets to define the official narrative, which will help him to maintain his grip on power.

In Animal Farm, Snowball is routinely used as a scapegoat after he is expelled by Napoleon. In Chapter Seven, for example, it is declared that Snowball is hiding nearby and "secretly frequenting" the farm every night. In these visits, it is alleged that he carries out all "sorts of mischief," like breaking eggs, blocking drains and trampling the seedbeds. In fact, every time something goes wrong on the farm, the animals immediately blame Snowball:

"Whenever anything went wrong it became usual to attribute it to Snowball."

This leads Napoleon to order a full investigation into Snowball's so-called acts of sabotage. Squealer concludes that Snowball is in league with Mr. Jones and that he has a number of "secret agents" on the farm. By scapegoating Snowball in this way, Napoleon is able to carry out a number of executions later in this chapter, on the pretense that he is ridding the farm of its enemies.

Snowball is easy for Napoleon to use as his scapegoat because Snowball is not there- he was "expelled" from the farm. Any time something goes wrong on the farm, the windmill falling apart, things disappearing, etc. it's easy to blame Snowball because he is not there to defend himself and the animals don't know any better so they believe it. It's also easy to use Snowball as a scapegoat in the sense that when his ideas are stolen by Napoleon, no one can say for certain that they were Snowball's ideas first. Napoleon even goes as far as to call Snowball a criminal and he relies on the ignorance of the animals and their inability to remember correctly to get them all to believe these things.

A windstorm knocks down the windmill which devastates all the hard work the animals have put in, all for the hope of making their lives easier.

They are told that it was Snowball's act of vandalism that did this to them. They even find that there are pig's tracks to back up the claim. A reward is offered for his capture. Instead of accepting defeat, the pigs try to instill anger to drive the animals to work even harder.