Short answers, pulled from the story.
The Baltimore riot of 1861 was a civil conflict on Friday, the 19th of April 1861, on Pratt Street in Baltimore, Maryland. It pitted antiwar Copperhead Democrats and Confederate sympathizers against Massachusetts and Pennsylvania militia regiments bound for Washington. It is also called the Pratt Street Riots and the Pratt Street Massacre.
Five soldiers of the 6th Massachusetts Militia were killed or mortally wounded: Corporal Sumner Henry Needham, privates Luther C. Ladd, Charles Taylor, and Addison Whitney, and Sergeant John Ames. At least 12 civilians were also killed, and about 36 men of the regiment were wounded. Luther C. Ladd is often called the first Union soldier killed in action during the American Civil War.
The riot happened because Baltimore was a largely pro-Southern city with divided loyalties as the Civil War began. A city ordinance banned steam rail lines through downtown, so the 6th Massachusetts Militia had to cross from President Street Station to Camden Station on foot, where a mob of Southern sympathizers attacked the soldiers with bricks, paving stones, and pistols.
The Baltimore riot of 1861 took place on Pratt Street in Baltimore, Maryland. The fighting began at President Street Station, spread through President Street and Howard Street, and ended at Camden Street Station, a route of about ten blocks between the two rail stations.
After the riot, Union General Benjamin Butler declared martial law in Baltimore on May 13, and Lincoln had the mayor, police chief, Board of Police, city council, and a sitting U.S. Congressman imprisoned without charges. Chief Justice Roger B. Taney ruled in Ex parte Merryman on the 4th of June 1861 that Lincoln's suspension of habeas corpus was unconstitutional, but Lincoln ignored the ruling.
Maryland did not secede after the Baltimore riot of 1861. Governor Hicks convened the state legislature in Frederick, where on April 29 it voted 53-13 against secession, though it also declined to reopen rail links with the North and sought to maintain neutrality.
James Ryder Randall, a Maryland native teaching in Louisiana who lost a friend in the riot, wrote the poem Maryland, My Maryland for the Southern cause in response to the violence, with the line Avenge the patriotic gore that flecked the streets of Baltimore. Set to the tune of O Tannenbaum, it became Maryland's state song in 1939 and was removed from that status in 2021.