The animals take the farm from the humans in chapter 1. In chapter 4, the humans return and try to take the farm back. Mr. Jones and "half a dozen others" approach the farm carrying sticks. Snowball has been expecting this, and, by way of preparation, has been reading all about the great military commander and strategist Julius Caesar.
When the humans enter the farm, they are attacked firstly by pigeons and geese. The pigeons attack them from above, and the geese peck furiously at their ankles. Snowball then leads a second attack, comprising himself, a donkey, a goat, and all of the sheep. The humans, however, appear to be too strong for the animals and manage to drive them back. At this point, Snowball gives a signal, and all of the animals seem to retreat. The humans give "a shout of triumph," thinking that they are going to win the battle.
However, what seems like a retreat proves in fact to be a clever strategy, devised by Snowball. The seemingly retreating animals lead the humans to the cowshed, where there is an ambush of more animals waiting. When the humans reach the cowshed, they are attacked from all directions. They are "gored, kicked, bitten, trampled." Snowball charges straight for Mr. Jones, and Boxer takes out a "stable-lad" with "his great iron-shod hoofs." The sight of the enormous and powerful Boxer is enough to frighten the rest of the humans into a real retreat of their own. They "make a bolt for the main road," pursued by a flock of angry geese, and then the whole battle is over.
After the battle, the animals celebrate by singing and hoisting their flag. They hold a funeral for the sheep who died in the battle, and then Snowball gives a speech in which he says that all animals must be willing to give their lives to protect the farm. Snowball and Boxer are awarded with medals for their outstanding bravery.