The Score
When a person is generally very astute, and possesses common sense and both self and worldly awareness.  For example, someone who is fairly well read, always up to date on current events, can carry on a conversation, and is able to think critically and form his/her own opinions while watching mass media with a critical eye, and is an overall competent individual in life, is someone that knows "the score".    People who "know the score" are also characterized by resourcefulness, and the ability to get things done no matter what.
Andrew is a very clever dude.  He knows the score.

Mark is a tool.  He doesn't have a unique thought in his head, and his common sense is lacking.  He doesn't know the score.