On Monday, May 4th, a protest was scheduled to be held at noon, as had been planned three days earlier. University officials attempted to ban the gathering, handing out 12,000 leaflets stating that the event was cancelled. Despite this, an estimated three thousand people gathered on the university commons. The rally was, initially at least, peaceful. The campus's iron victory bell was rung to signal the beginning of the rally. The rally may have in fact been legal, since a state of emergency had not been declared, but there was a widespread belief among both the students and the guardsmen that the rally was illegal.

Just before noon the Guard ordered the crowd to disperse and fired tear gas. Because of wind, the tear gas had little effect on dispersing the crowd, some of whom were now responding to the tear gas with rock-throwing and chants of "Pigs off campus!" Some students began to pick up the tear gas cannisters and throw them at the National Guardsmen.

A group of seventy National Guard troops advanced on the hundreds of protesters with fixed bayonets and with their weapons locked and loaded, in an attempt to disperse the crowd. The National Guardsmen were wearing gas masks and had little training in riot control. They soon found themselves trapped on an athletic practice field which was fenced on three sides, where they remained for ten minutes. The Guardsmen then began to withdraw back in the direction from which they had come, followed by some of the protesters.

When they reached the top of a hill, 28 of the seventy guardsmen fired a fusillade of between 61 and 67 shots at the unarmed students. Although the firing was later determined to have lasted only 13 seconds, a New York Times reporter stated that "it appeared to go on, as a solid volley, for perhaps a full minute or a little longer." The question of why the shots were fired has been widely debated. The Adjutant General of the Ohio National Guard told reporters that a sniper had fired on the guards, but this was later shown to be false. Many guardsmen later testified that they were in fear for their lives, although the distance of the students at that point makes the claim seem unlikely.

The shootings killed four students and wounded nine. Only one of the four students killed was participating in the protest, and one of the students killed, William Schroeder (who was observing but not participating in the demonstration) was a member of the campus ROTC chapter. Of those wounded, none was closer than 71 feet (22 m) from the guardsmen. Of those killed, the nearest was 265 feet (81 m) from the guardsmen.

Killed:

* Allison Krause
* Jeffrey Glen Miller
* Sandra Lee Scheuer
* William Knox Schroeder

Wounded:

* Alan Canfora
* John Cleary
* Thomas Mark Grace
* Dean Kahler
* Joseph Lewis
* Donald MacKenzie
* James Dennis Russell
* Robert Stamps
* Douglas Wrentmore

Immediately after the shootings, many angry students were ready to launch an all-out attack on the National Guard. Many faculty members, led by Glenn Frank, pleaded with the students to leave the Commons and to not give into violent escalation. After 20 minutes of difficult speaking, the students left the Commons. Ambulances came and tended to the wounded, and the Guard left the area.