get (one's) head in the game

1. To focus on and put one's best effort into the athletic match currently underway. We're down by two points, and you're having trouble remembering the plays I'm calling? You need to get your head in the game, Jenkins! I was so distracted by seeing my ex-girlfriend in the bleachers that I just couldn't get my head in the game. If you're a professional athlete, you need to be able to get your head in the game no matter what is going on in your personal life.

2. By extension, to focus on and put one's best effort into some task or endeavor at hand. I know you've got some issues at home right now, but you've got to get your head in the game. If we don't close this deal today, the whole company goes under! Did you see all the evidence the defense attorneys produced? If you don't get your head in the game, we're going to lose this case! Even as an intern, I knew I needed to get my head in the game and impress the head of the department.