game face

Noun

 * 1)  The expression of one who is prepared for or is facing a lot of difficult and/or undesirable work, especially when it is imminent.
 * The editor told his star reporter to put his game face on, because he was going to cover a potentially hours-long city council meeting where they were going to discuss the controversial issue and tempers were expected to flare.
 * 1)  A facial expression used to prevent giving away one's emotions.