In flyball we obviously want the tug to be the highest value thing..the ultimate reward for a job done well. The ball on the other hand is something we want them to be willing to put in their mouth in order to get the big reward. We don't want them to savor the moment of getting the ball out of the box, but rather the box should be something that they want to get away from as quickly as possible. Dogs that tend to spit balls early are faster than those that chomp on the ball all the way back and don't spit for the tug. I will never understand why some people YELL at their dog to drop the ball and TUG! Or those that wave the tug in the dogs face while the dog is chomping the ball until it's time to run again. The dog in these examples did not get a reward.
New people to flyball often think of flyball as a sport that is great for dogs that love tennis balls. I think it's more of a sport that is great for dogs that thrive in overstimulating environments, love to be with their handler and willing to work hard to tug.
The key parts of starting out a puppy are building tug drive, building value for being with their handler and dealing with very distracting things. Until you have a dog that can tug with enthusiasm in the presence of balls rolling, dogs running, people running, loud noises and other flyball craziness, you are not ready to introduce other parts of flyball, especially the ball retrieve. In training for flyball I find the ball to be an afterthought in the early stages of training. It doesn't hurt to do flat recalls with a puppy with balls rolling everywhere as a prevention for ball obsession.
This early training needs to be happening at home as well. Lots of tug building activities and most importantly lots of time spend interacting with the handler. I don't agree with the idea that tennis balls should be restricted. It doesn't make logical sense to me as a method to reduce the value, but I do think that the dog shouldn't be encouraged to find value in chomping any toy including a tennis ball my himself.
If your dog is already obsessed with tennis balls. It might be hard to fix, but at least you know that your dog finds SOMETHING valuable and has drive. It's just for the wrong thing. I've come to realize that it's not helpful to use "leave it" with balls on the ground because people don't tend to train a solid enough leave it so that the dog WANTS to leave it. It's more of a replacement for "NO". I haven't found that pool noodles are helpful.
Here are some ideas:
1. Teach a SOLID recalls. Extremely solid. You should be able to bet $100 that every time you call your dog he will come to you in all situations. With the ultimate challenge being his ability to recall to you past a ball on the ground or several balls being scattered on the ground.
2. Teach a solid "drop it" command using the technique HERE . This will help with the dog to drop the ball quickly and possibly go for the tug (depending on tug drive). It doesn't help with balls in the run back though. Also to teach "drop it", when the dog brings the ball to you (if he doesn't bring it train him in a small enough area on a leash so that he does) grab him by the collar and put your hand on the ball without tugging and wait patiently. As soon as he releases it, throw it again as a reward. Repeat
3. Toy exchange game. Take out 2-4 toys (no balls to start) and spread them around the training area with no other distractions to start. Pick up one and start flipping it around and act like it's the coolest thing ever. As soon as your dog comes over and starts playing with it and tugging drop it and run to the next and do the same thing. Keep switching to the next toy so that your dog learns that the most fun toy is the one that you have. Eventually add balls into the mix when your dog is reliably going for the toy that you have rather than the ones on the ground.
4. Use the ball as a reward in your training. Instead of keeping balls away from the ball obsessed dog, use a ball as a reward for the behavior that you eventually want - enthusiastic tugging. With the dog on a leash and a ball in your pocket, tug with the dog with no balls in his view. When he is tugging to the level of enthusiasm that you want (this shouldn't take more than 30 seconds), say "OK" or other release word and place the ball on the ground for him to get.
Refer to # 2 on this list to get the ball back from him. Put the ball back in your pocket or hide it with easy access and repeat. If the dog tugs for 3 seconds and then looks for the ball, he doesn't get it. ou decide when he gets it.
You can advance this game by releasing him to a ball you throw or several balls to choose from and eventually without a leash. Eventually you will find that when you say "OK" and throw the ball, he will chose the tug over the ball. It takes time though.
If the dog is already doing box work, you can play the same game. Require that your dog tugs with you and then release him to get the ball from the box when you are happy with his tugging. In this situation tugging after the ball would be ideal too. Make sure he can't reward himself with the ball, by having the box loader put the ball in just as you release the dog.
5. Premack. This is similar # 4, but only works if you use something that is currently more valuable than the ball. With the dog on a leash and lots of high value treats, click/treat when the dog looks at you. When he is doing this reliably, put a ball on the ground and wait for him to look back and you and reward him with a click/treat. After doing this for a few sessions, after you click/treat for orienting to you, say "OK" and let him get the ball if he wants. And then wait. While you are waiting you are holding his leash and not moving or saying anything at all. At this point he has to decide between standing there playing with the ball by himself without moving more than a few feet or looking at you and getting a treat. After a few times of trying this, he will likely find the ball less rewarding in this situation than the high value treat. As he gets more reliable with this, start lowering the value of the treat or use a tug instead of food and increase the value of the ball by giving him a long line, taking the leash off in a small area, throwing the ball etc.
7. Self Control. Teach your dog impulse control. I use Susan Garretts game "It's Yer Choice". to teach my dogs to not steal food. It can be expanded to teach them not to steal toys or basically that they have to "work" to get something they want. They chose to either do what you want them to do and get their reward or neither. In this case you can require that your dog does a basic command (nose touch or sit/stay) and gets a ball as a reward or if you want him to leave the ball practice this game and give him a very high value food reward for choosing to not go for a ball.
8. Balls in the Crate. I'm not sure how well this works, but I've that some people have had success with filling the dogs crate with balls with the thought that eventually he will be annoyed by them rather than excited about them.