Although sometimes appropriate, passive verbs are generally considered weak and wordy. Active voice is much more effective and clear. We know from reading this that Bill is the one who threw the ball. He is the agent doing the action of the verb.
Passive voice changes that direct action.
The ball was thrown by Bill to his son. Notice that the basic information is the same. Passive voice may not change the meaning of the sentence. Not all passive voice is awkward. We can make this sentence smoother and less wordy by eliminating some information.