[We] marched to Gettysburg and when wee got thare wee formed A line of battle and soon the ball opned […]
The phrase “the ball opened” was much used and well understood by Civil War soldiers and civilians alike. It referred to the moment a battle began, or, more specific, to the moment the balls – meaning the projectiles – started to fly. It is mostly used in reference to the individual describing the action. In the quote above, the battle of Gettysburg had started hours before, but “the ball opned” for Private Coghill of the 23rd North Carolina Infantry when he and his comrades were hit by a volley from the men of Baxter’s brigade hinding behind a stone wall on Oak Ridge.
The expression can be found in countless letters, diaries and memoirs. “The ball is opened again and we are, from what I see, to have another hot day”, Maj. Joseph H. Chennoweth of the 31st Virginia wrote when he marched into battle in the Shenandoah Valley on June 9, 1862. “On our right the ball has opened and heavy cannonading is now (3 PM) going on and off,” wrote Union artillery officer John Cheney during the Chattanooga campaign of November 1863. And again at the battle of Gettysburg, a private of the 150th Pennsylvania even taunted the rebels by shouting: “Come boys, choose your partners! The ball is about to open! Don’t you hear the music?” 
But why did those soldiers compare a battle with a ball, a social event that is usually seen as festive and cheerful?
On a first, superficial level, calling a battle a “ball” is an euphemism. The soldier is playing “old hand”, he is signalling his knowledge of military jargon and, at the same time, presenting himself as distanced from the dangers and horrors of the battlefield. He shows that he can make light of the horrors of war and therefore remain in control of his emotions – a central part of Victorian manliness. 
But may there be a deeper meaning to this metaphor? To answer this question, it would be interesting to trace the origins of the comparison. And indeed there is a piece of text that may have been the source of the phrase: namely a letter by one of the most famous generals of the time, the victor of Waterloo, Arthur Wellesley, 1st Duke of Wellington. This letter was written on August 8, 1815, less than a month after the battle, in answer to a request by an unknown writer – some think it might have been the novelist Walter Scott.
It seems that the inquirer presented a plan to write about the battle the general had just fought. This is what Wellington answered:
I have received your letter of the 2d, regarding the battle of Waterloo. The object you propose to yourself is very difficult of attainment and, if really attained, is not a little invidious. The history of a battle, is not unlike the history of a ball. Some individuals may recollect all the little events of which the great result is the battle won or lost, but no individual can recollect the order in which, or the exact moment at which, they occurred, which makes all the difference as to their value or importance.
What did Wellington mean? By drawing the comparison to the swirling social dynamics of a ball, he stresses the impossibility of describing a battle in its entirety, of giving a complete picture of what happened at a specific moment in time. Like a ball, a battle is an overwhelming experience that consists of many tiny occurences which are difficult to bring into order once the event is over. Wellington, the man who commanded the allied armies at Waterloo, in a way acknowledged the impossibility of giving a complete account of that event.
Of course I don’t know if this quote really is the origin of the comparison between battle and ball as it was invoked during the Civil War. The letter containing the quote was printed in at least three books that were widely disseminated before the war: it appeared in Edward Cotton’s A Voice from Waterloo (first published in 1846), Macaulay’s History of England (1848) and Clark’s Battles of England and Tales of the Wars (1848). It was also published in periodicals, such as The Athenaeum (November 17, 1838) and The Monthly Review (1839). We also know that Civil War soldiers liked to read books on military history and strategy and that works about famous generals were especially popular. So there might well be a connection between Wellington’s letter and the widespread use of the phrase during the Civil War.
In this light, the comparison between ball and battle may be more than just an euphemism. It may hint towards the deeper truth, namely the difficulty, maybe even the impossibility of giving a complete account of the events that happened in a battle.
This is something to keep in mind when reading or writing about history.
 Pvt. Jonathan Fuller Coghill, Company G, 23rd NC Infantry, July 9, 1863, available online at the Private Voices project.
 Cozzens, Peter: Shenandoah 1862. Stonewall Jackson’s Valley Campaign. Chapeh Hill, NC: University of North Carolina Press 2008, p. 488; Armstrong, Gordon (ed.): Illinois Artillery Officer’s Civil War: The Diary and Letters of John Cheney. College Station: virtualbookworm.com 2005, p. 195; Martin, David G.: Gettysburg, July 1. Cambridge, MA: Da Capo Press 2003, p. 175.
 Foote, Lorien: The Gentlemen and the Roughs. Violence, Honor and Manhood in the Union Army. New York: New York University Press 2010, p. 57.
 Cotton, Edward: A voice from Waterloo. A history of the battle, on the 18th June 1815. London: B. L. Green 1849, p. 225-226.
 Kaser, David: Books and libraries in camp and battle. The Civil War experience. Westport, Conn.: Greenwood Press 1984, p. 16f.