There is no reason for your integer to be stored as a pointer. Change your property to:
@property (nonatomic, assign) NSInteger highScore;
you also don't need to synthesise it, so remove that (the compiler does it for you, and it does a better job).
Then change your user defaults code to:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
[defaults setInteger:highScore forKey:@"retry"];
[defaults synchronize];