I don't usually watch 'reality' television, but I enjoy History Channel's Top Shot because it is based on concrete shooting skills instead of deviousness or popularity. Week after week, contestants compete in a variety of target shooting and either perform or go home. One thing that stuck in my head is during the show's introduction, the announcer says, "There are shots that changed history..."
Were there shots that changed history? I think so. Unfortunately, for one shot to change the course of a battle or war, it generally means that one shot had to kill someone strategically or politically important. Depending on what side of the conflict you're on, it's either a victory or a tragedy. But I think we can divide these historical shots into two types--those that took place during wartime against military leaders, and assassinations of political leaders whether in peace or war.
An early instance of the military model would be the Battle of Hastings in 1066. While the Normans under William were attacking uphill against the Saxons, a Norman arrow hit Saxon King Harold in the eye and killed him. It isn't known who fired the specific arrow, but the death of King Harold certainly dismayed the Saxons and threw them into confusion and eventual defeat. A single arrow opened the way for the Norman conquest of England.
A second example is the naval battle of Trafalgar in 1805 during the Napoleonic wars. Admiral Nelson, a genius of sea combat, led his ships against a French fleet. While the two fleets hammered each other at close range, Nelson was shot with a bullet (not a cannon ball) and died on the deck of his ship Victory. While the British won the battle, the loss of Nelson may have lengthened the wars with Napoleon.
In the second model, we have history changing shots of a more political nature. Usually these came in the form of assassination, whether by conspiracy or an individual. The assassination of Abraham Lincoln may not have affected the outcome of the Civil War, but did affect the crucial Reconstruction era after the war. The assassination of US President John F. Kennedy ensured he would not have a second term in office, and probably had important repercussions in the growing US involvement in Viet Nam. The shooting of Egyptian President Anwar Sadat in 1981 by troops who opposed his peace agreement with Israel certainly affected the overall stability in the Middle East and future of Egypt.
So while war and assassination are not civilized ways to bring about change, there is no doubt we can point to specific shots that changed history. And on a side note, it's interesting that the person who made each of those shots is often forgotten, while the person who died is remembered.
(The pic of the musketeer is found here. Some info drawn from WAR THROUGH THE AGES by Lynn Montross.)