Our beautiful boy, 8 months old springer spaniel has become ball obsessed . He just goes into a trance every time a tennis ball is around. He is normally an absolute delight, loving, cuddly, loves to play with other dogs and children, likes to chew toys and loves treats, the friendliest dog ever. Unless……there is a ball present!!! Then he will go into a trance and has eyes only for the ball, completely loosing interest in everything else. He looks crazy !! 
He expects us to throw the ball over and over again in a non ending game of fetch. He could go on all day with no other interaction if we would only ‘play ball’
We are now hiding the ball and only bringing it out on walks however I do feel mean and feel sorry for him, as he carries on looking for it for a while but it is the only way to have our lovely, friendly dog back.
Is this normal ? Please help !!