That simply says that players will be an array of Player. It doesn't specify how large that array will be, so by default its of size 0. Before trying to read or write to the array you must specify the size of it:
players = new Player;
For example. Arrays do not allow you to resize them; this process must be done manually. If you want to be able to dynamically manipulate the array without too much overhead, look at using collections instead. ArrayList, Vector and LinkedLists are all good alternatives depending on what you want to do with them. Each one has a specific purpose for which they shine, but typically speaking the ArrayList and Vector will be the two most interested in. LinkedList is actually wonderful for creating a cyclic queue btw, so if players are round robin in actions, a LinkedList may be a perfect choice (also look at the queue / stacks [actually I'm not 100% sure java has a queue class - there is a priority queue, but that's not quite the same. I'm quite sure it has a stack]).