It's perfectly normal for a puppy or dog to growl when playing tug of war. You need to be aware that growling is a warning of aggression and that your dog could attack or bite!

You need to be aware if the growling is appropriate or inappropriate. If your puppy or dog is eating or chewing on a favorite toy and growls when you come near, that isn't behavior you can tolerate. It's the sign of an aggressive dog.

If the growling begins unexpectedly with no obvious trigger, a visit to the vet is called for to make sure there isn't a medical reason.

Growling can be a signal that your dog is trying to position himself as the alpha dog or pack leader. So, the next thing you check is that you are the pack leader in your home. This will set a firm foundation which can solve many behavior problems.

To set yourself as the alpha dog, you should adopt the approach of NILIF (Nothing In Life Is Free). This means that before you give your dog anything, he must obey a command. With this approach, you can't allow your dog to demand attention from you. If you allow him to demand attention, you have lost dominance. Just ignore him when he pushes you for attention. You should choose when to give him attention. He may try harder but you must not give in or all is lost.

With NILIF you and everyone in the home need to be consistent and persistent.

So, for example, you should ask your dog to sit quietly before you place his food down or before take him out for a walk. Don't allow your dog to offer a behavior before you ask for it - that doesn't count.

Make sure that when leaving the house, you walk through the door first. You can let your dog see you eating a small snack like a biscuit before you put down his food since the alpha dog eats first. You are only required to repeat this for two weeks to position  yourself as the leader of the pack.

Everyone in the family needs to engage in similar processes to set them higher up in the hierarchy than your puppy or dog.

The alpha dog makes his bed on higher ground, so do not allow your dog to get on your bed if you want to be higher in the hierarchy.

You should do regular training in obedience with your puppy or dog. Make the training sessions short and fun. This will help in making your dog better behaved in general.

Read more about how to stop your dog growling and other aggressive dog behavior.