I've re-trained retired greyhound racers for family life for a few years. Some dogs just don't like to play, especially if they'd been abused. One thing to try is to take something fillable, like a Kong, and put small kibbles into it. This will encourage the dog to at least have some interest. You can also try tossing the Kong and seeing if they'll go get it. Another trick is to but peanut butter on the outside of a hard toy and play with it outside (sure can make a mess). Some dogs love to "kill" the squeeker inside a plush toy and will start playing that way, especially if you make it squeek. Lots of praise when playing is VERY important. This is a very long process and the dog may not ever play. Keep in mind, a dog abused into submission will rarely rough house with the human. My greyhound rarely plays and when he does it's just for very short periods of time. Good luck, but love the dog whether it plays or not. There's got to be other joys it gives you.