Trouble with Core Data

Ok I am trying to grab a NSMutable Set. Yes I have a previous post on this but this is slightly different. I have A player entity and a team entity. It is set up as a one to many relationship... On a different view controller I added players to the team. Now I am trying to get that teams players to show up on a table view... I am fetching the information as follows.

Code:

    - (NSFetchedResultsController *)fetchedResultsController {
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    
    NSString *entityName = @"Team"; 
    NSLog(@"Setting up a Fetched Results Controller for the Entity named %@", entityName);
    
    // 2 - Request that Entity
    
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];
    
    AppDelegate *delegate = [[UIApplication sharedApplication] delegate];
    _managedObjectContext = delegate.managedObjectContext;
    
    // 4 - Sort it 
    request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"players"
                                                                                     ascending:NO
                                                                                      selector:@selector(localizedCaseInsensitiveCompare:)]];
    
    // 5 - Fetch it
    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                        managedObjectContext:self.managedObjectContext
                                                                          sectionNameKeyPath:nil 
                                                                                   cacheName:nil];
    _fetchedResultsController.delegate = self;
    
    return _fetchedResultsController;
}   

Then on my cell for row at index path I am setting the Player object to the fetched results as follows

Code:

        Player *p = [_fetchedResultsController objectAtIndexPath:indexPath];
Then, I am setting the title of the cell like so.

Code:

    cell.textLabel = p.firstName;

I am getting the error

Code:

reason: 'to-many key not allowed her

I am wondering what am I doing wrong???