The previous human owner of the Manor Farm, Mr. Jones, had never given up hope that he would reclaim his property from the animals. So, Jones and his men, "with a half a dozen others from Foxwood and Pinchfield," prepared to take back the farm. Jones carried a gun, but the others were armed only with sticks. But the animals were waiting. Snowball launched an attack, first with pigeons and then geese. After the men scattered the fowl, they became overconfident, Snowball sent in another group of animals, led by Boxer, and within five minutes the men had scattered. One man was injured, and one sheep died. The animals had won the Battle of the Cowshed.
The Battle of the Cowshed happens in Chapter 4.
The reason for this battle is that the human farmers who own the farms around Animal Farm are getting worried. The animals on their farms have been singing "Beasts of England" and the farmers are worried that their animals will rise up next. So they invade Animal Farm to try to take away the animals' new freedom.
The result of this battle was that Animal Farm won and remained "free." Snowball was the main hero for the animals. The animals got a trophy, too. It was Jones's rifle which they found lying on the ground kept as a memento of their victory.