Obviously we can see by being run off the farm that Snowball was an ineffective leader.
So, he was removed by someone more powerful and therefore lacked power, but why? Why didn't anyone fight for him?
I think if you take a look at the committees Snowball tried to create and the language he used with the animals and the response they produced to each, you will find your answer. He could have been a great leader, but would not come to meet them at their point of need. They wanted to trust him, but could not understand him. You can find quotes to support these 3 claims on pages 32-34 of the Signet Classics edition of the book.
His committees had great vision, but the purpose was not articulated in a way that the animals could comprehend.
Snowball is also an intelligent, well-spoken debater who has a knack for reading and leading other animals. In the Battle of Cowshed he has learned his successful military strategies from reading Julius Caesar. He also leads the animals in the initial attempts to “industrialize” Animal Farm by designing the plans for the windmill. However, he is ultimately absent from a leadership role after being run off the farm by Napoleon and his dogs. Napoleon feels threatened by Snowball’s popularity and feels the need to exile him just as Lenin did to Trotsky.
In this chapter, the animals are forced to fight in the Battle of the Cowshed against humans from the nearby farms. In this battle, Snowball turns out to be a very good military leader. He makes all the right tactical moves. He is also somewhat brutal, thought.
We can see that Snowball is a great military tactician because he completely fools the humans. He pretends to have the animals retreat but then counterattacks at just the right time.
We can see his brutality when he tells Boxer to stop feeling sorry for the person he thinks he has killed. He says that the only good human is a dead human and that there is no place for "sentimentality" in war.