The Battle of Cowshed occurred because Mr. Jones finally was able to get a group of men together to attempt to take back his farm. At first, no one wanted to help Jones. In fact, Orwell states that people wanted to take advantage of Jones's situation. However, when the rebellion seemed to be going well, others were afraid that this rebellion might spread.
Snowball got wind of this and he was ready. He studied the battle tactics of no one less than Julius Caesar. Snowball's tactic was threefold.
First, he sent the pigeons to create disorder among the attackers. Then he sent the geese to peck at the legs of the people. All of this was diversionary. Second, Snowball sent bigger animals like Muriel, Benjamin, and the sheep. After this initial attack, Snowball ordered them to retreat. The humans thought they won. They even rejoiced. However, this retreat, too, was all a part of his plan. Third, as the men came closer, the horses and cows moved into the battle and surprised and overwhelmed Jones and his men. Here is the text:
As soon as they were well inside the yard, the three horses, the three cows, and the rest of the pigs, who had been lying in ambush in the cowshed, suddenly emerged in their rear, cutting them off. Snowball now gave the signal for the charge. He himself dashed straight for Jones.
The battle was successful.
Jones was hurled into a pile of dung and his gun flew out of his hands. But the most terrifying spectacle of all was Boxer, rearing up on his hind legs and striking out with his great iron-shod hoofs like a stallion. His very first blow took a stable-lad from Foxwood on the skull and stretched him lifeless in the mud. At the sight, several men dropped their sticks and tried to run.
The animals rejoiced. Surprisingly, there was only one casualty - a sheep. The animals gave him honors. Also they decided to call the battle, "Battle of Cowshed," because that was where the battle was fought. At this point, Snowball was also recognized for his heroic role in the battle. Perhaps more importantly, October 12th, the date of the battle, would become a lasting memory for the animals.