Shootout is one of the 4 games available with the Shooting Gallery add-on. Three of the games use game cart #9 and the fourth uses #10. The add-on comes in its own box with a gun!

Extract from Chronogamer blog:
"Shootout involves moving your little white square from window to window (starting at the upper left to the upper right, cross the street to the lower right then make your way to the lower left) while your friend, parent, spouse, offspring or other loved one tries to shoot you. The person playing the "outlaw" who sneaks from window to window, can't just zip through the window at a blinding speed. The "outlaw" has to stop in the window long enough to say "You'll never get me, Sheriff!" (also pronounced "yoollne'ergitmesherff!" when the outlaw is in a big hurry) during which speech the "sheriff", with the big gun, is given a realistic amount of time to try to shoot them. This IS a fun game!"