play mind games

1. To engage in psychological manipulation or intimidation with the goal of undermining someone's performance or confidence. The boxer is notorious for using obnoxious and belittling taunts to play head games with his opponents. She's going to try to play head games and psyche you out, but just focus on what you came here to do. Don't mind games with yourself. If you're in your own head telling yourself that you can't do it, then you have no hope of succeeding.

2. To use one's thoughts to encourage or convince oneself of something. Of course I'm nervous before a big game! I just play head games with myself so that the negative thoughts don't paralyze me when I'm out on the field.