Although Rhodes had failed to pursue his stated intention of obtaining a court order declaring a state of emergency, it was widely assumed that martial law was in effect and that control of the campus rested with the Guard rather than with university officials. Demonstrations were banned, but, despite the distribution of 12,000 leaflets announcing that prohibition, many students were unaware of it when classes resumed on Monday, May 4. By noon on that clear brisk day, perhaps as many as 3,000 students congregated in and around the Commons. Gathered around the Victory Bell, roughly 500 of them were actively protesting Nixon’s expansion of the war and the presence of the National Guard on campus. Another ring of about 1,000 individuals cheered their efforts, while some 1,500 more students watched from the periphery. Across the Commons, by the charred remains of the ROTC building, more than 100 Guardsmen under the command of Brig. Gen. Robert Canterbury confronted the demonstrators with Garand (M-1) rifles loaded with live ammunition.

Canterbury’s order that the demonstrators disperse, delivered from a jeep at about midday, was greeted with chants, insults, and rock throwing. After launching tear gas at the demonstrators near the bell, the Guardsmen began advancing with bayoneted rifles across the Commons in two groups. The smaller contingent swept up the left flank of the slope, forcing demonstrators back and blocking the passageway between Prentice Hall and Taylor Hall to the east. Meanwhile, the larger force marched up Blanket Hill to the west of Taylor Hall, with demonstrators parting or retreating up and over the hill. On the other side of Taylor Hall, the Guard descended onto a football practice field that was fenced on three sides. The most aggressive demonstrators were in the parking lot of Prentice Hall, several hundred feet away from the Guard, so that most of the rocks they threw fell short of their target. More students lined the grounds around Taylor Hall. During their 10-minute stay on the practice field, a number of Guardsmen knelt and aimed their rifles at demonstrators. Another group of Guardsmen huddled briefly (later prompting speculation that in that moment they had conspired to shoot at the demonstrators).

Having effectively dispersed the demonstration but feeling threatened, the more than 70 Guardsmen in this contingent began retracing their steps up the reverse side of the hill toward the Commons. At 12:24 pm, as they reached the crest of the hill near an umbrella-like concrete architectural feature known as the Pagoda, 28 Guardsmen quickly wheeled back and over the next 13 seconds fired between 61 and 67 shots. Many of the Guardsmen discharged their weapons into the air or at the ground, but a number of them fired into the crowd. Four students were killed and nine others were wounded (one of them paralyzed from the waist down). Two of those killed, Jeffrey Miller and Allison Krause (who fell about 265 feet [81 meters] and 343 feet [105 meters] away from the Guard, respectively), had been actively involved in the demonstration, but the other two fatalities, William Schroeder and Sandra Scheuer (both shot at a distance of about 390 feet [119 meters]), were bystanders on their way to class. The closest victim of the shooting, Joseph Lewis, had been standing about 60 feet (18 meters) away from the Guard. Later there would be much debate over why the Guardsmen had fired—whether they had been ordered to do so, whether they thought they had been fired upon themselves and shot in self-defense, or whether a small group of them had indeed conspired to shoot.

In the chaos that immediately followed the discharge of the weapons, the Guard returned to the Commons, surrounded by an enraged throng whose belligerence threatened to explode into violence that might have been answered by another fusillade by the Guard. At this combustible moment, faculty marshals, led by Glenn Frank, a geology professor, successfully persuaded the students not to endanger their lives by taking on the Guard. The Commons was evacuated, and Kent State Pres. Robert White ordered the university closed (which it effectively remained for some six weeks).