Hit a home run

Sometimes, the batter hits the ball so hard or so well that he or she is able to run around the entire diamond before getting an out, scoring a run on the first hit. This is called a home run. Most home runs are the result of the ball being hit past the fence at the back of the outfield, at which point its completely out of play and all the fielding team can do is watch.
A home run hit while the bases are loaded is called a grand slam. Obviously, a grand slam is worth four points (one for each runner), and can turn the tide of a difficult game or virtually guarantee victory. Grand slams are exceptionally rare, but very exciting.