At which Civil War Battle did Stonewall Jackson get his nickname?

The First Battle of Bull Run or First Battle of Manassas, was fought on July 21, 1861 in Virginia. The Union troops, 35,000 strong, under the command of Brig. Gen. Irvin McDowell engaged the Confederate troops, 20,000 strong under the command of Brig. Gen. P. G. T. Beauregard. Both armies were inexperienced, not much more than raw recruits. The battle initially went well for the Union until a Brigade of Confederate (1,500-4,000 men) reinforcements arrived, under Brig. Gen. Joseph E. Johnston. The battle changed decisively in favor of the Confederates who ended victorious.

This battle is also known as the "picnic battle". Because of its close proximity to Washington many civilians and powerful Senators brought picnic baskets to enjoy the spectacle but were forced to scramble back to Washington in fear for their lives.

During a particularly fierce Union assault, as the Union was about to break their lines, Brig. Gen. Barnard Bee, looked over and yelled to his men "look men, there is Jackson just standing there like a stone wall", the name stuck. After being inspired, the Confederates charged the Union line, overran it, captured guns, and changed the course of the battle.

Thomas Jonathan Jackson, a graduate of West Point and former professor at the Virginia Military Institute was a Brigadier General at the time but rose to the rank of Lieutenant General before he was mortally wounded at the Battle of Chancellorsville in Virginia in May 1863.