Welcome Sheezza! Does he always go for the ball, or just sometimes? If he always goes for it, but just doesn't bring it back, then work on "give" or "drop it." Have the ball in front of you, and click and treat for any interest in it. (Looking at it, nosing it, picking it up) When he picks it up, offer a treat or a more interesting toy and say, "Give." Reward him heavily when he releases the ball. If you're using treats, use a VERY high value treat. Rolled dog foods, freeze-dried liver treats, hot dogs...these are all high value treats that most dogs go crazy for.
What do you do when he runs away with the ball? If he runs away with it and you chase him around yelling, "Bring it here, bring it here!" you are accomplishing nothing. My Rottie mix looooves a game of getting the ball, making laps around the yard, and trotting back to me when I ignore him as if to say, "Okay, I'll be good, just play with me!!!" He's a goof. Anyway, when he gets the ball and brings it back, that means the game continues. Give him lots of praise when he gives it back. If he runs around with it, the game is immediately over. Ignore him entirely and walk away, perhaps into another room. Never give him any type of reward(chasing, talking, treats, etc) when he runs away with the ball. Just end the game. Start back maybe 5 minutes later and use the same rules.
Hope this helps! Welcome to the Academy!