In baseball a full count is when the batter has 3 balls and 2 strikes. If another ball is thrown without the batter swinging, its a walk (batter automatically gets to 1st base). If another strike is thrown and the batter swings and misses or doesn't swing and the ball is in the strike zone, thats strike 3 and the batter is out. If a foul is hit and not caught the batter continues. The batter could hit as many foul balls and not be out if the ball is not caught. A foul counts as a strike except on the third strike.
the full count is a variation on the shocker. the pinky and ring finger are inserted into a woman's ass while the middle finger, index finger, and thumb of the same hand are inserted into her vagina. this is called a full count because of the distribution of the fingers, three in one hole, two in the other. it is a reference to a three ball, two strike count in baseball, called a full count. the term is also appropriate because the woman, upon the execution of the full count, is full of fingers. you must be especially dexterous to perform the full count. it requires an awkward and difficult positioning of the fingers.
the expression is used in such a context as: "liam gave katie a full count last night, she was pleasantly surprised at his use of such an expert maneuver".