Chicago Area People - question

Hey guys! Question for you. My friend, Mike, is going to be in Chicago for a series of baseball games in mid-May. All the hotels he can afford are all around O'Hare and he needs to know if it's easy to get from the hotels by the airport to the baseball field - like easy public transportation especially since he will most likely be drinking.

Any information I can pass on will be greatly appreciated!

Thanks!