first of all if you have only had him a few days then he need to learn to respect you and see you as the pack leader, before he will give you anything.

Being the pack leader:
you need to be firmer with him and become the dominant party, using some simple exercises that you can do in your own home. you need to stand tall without being ridged and you need to relax at the same time. you must never back down to him and walk away, because in the dog world this means that you have submitted and backed off and he has won. you need to always be calm and assertive when doing any exercise with your dog. you can practice dominance when out on walks. dont let him got out of the door in front of you and dont let him walk in front of you unless you give him the leway. keep the lead short, relaxed and keep moving forward, dont let him stop and sniff the ground unless you let him.

before you continue to play ball with him you can do an exercise on the lead in your garden or home, but with a twist. you can put the ball on the ground, and some other toys that he likes. they must be about a meter apart for this to work and for him to achieve in this exercise. once you have the toys in place, put some pebbles, rice, coins or anything you can think of that will fit in the bottle and rattle, in a small plastic bottle and put the lid on it. you then have got your startle tool, without this costing you anything. you can then put your dog on his lead and take him outside. make him sit and if he attempts to get close to or take the toys then you must correct him with your bottle, shake it and he will stop and wonder what is going on, this will snap him out of trying to take the toys for a small amount of time.
you can then walk him past the toys, but everytime he gets too close, looks at the toys or even tries to take them, then you must firmly shake the bottle. when you shake the bottle, you must say leave it everytime for this to work. this will take time, but will be very effective. if he leaves the toy and walks past it, praise him and give a treat. you can walk him up and down past the toys for as long as you like but you must correct him everytime he pushes his luck.
he will soon learn leave it and will then start to avoid the toys when you walk him past them, you will also notice that he will be more focused on you and the walk, not the toys. when you are at this stage you can reward him with love and a treat.

now for the next part:
if you have done the exercises right he will now respect you as the pack leader and listen to you more, when you tell him what to do or not to do.
now you can play with him and through the ball for him, when he brings it back to you, you need to stand tall, keep calm and assertive and step forward, tell him to leave it. if your training has been successful then he will back off, if he does this then you can pick up the ball and reward him with a treat and continue playing without the annoyance of him not giving you the ball or other toys.

for other traing you could try clicker training, because this is instant positive reinforcement!

i have used these techniques with previous dogs and they work, as long as you are patient and take the time to train him in this way.
if you need any more help then please feel free to contact me