That is a brave and loyal cat. It's interesting if you stop the action every few frames to see what is happening. The cat charges at full speed and rotates to the right at the last second, giving the dog a full-on body blow, transferring all of it's momentum to the dog and knocking it free from the child. The dog runs off and when the cat sees the child is safe, he gives chase to the dog, scaring it away for good, then quickly returns to the child's side. If the cat's intention was to attack the dog, it would have dove into the dog, claws first; but that clearly wasn't the cat's intention. The cat was only concerned about the child's safety.