60's revolution?

HINT: United States v. O'Brien...

There were significant turmoil in Czechoslovakia and France in 1968, but in neither case do i know May 28, 1968 to have been significant. The only event which i thought might apply was the rioting in Louisville, Kentucky, but what i find online shows the incident sparked on May 27, 1968, with violence in the streets (but not particular outstanding event) on May 28, and the police finally getting a grip on it by May 29.

I did look online for the student uprisings in France in 1968, and don't find any particular significance for May 28. Neither did in find any particular significance for that date in Czechoslovakia, during the 1968 "Prague Spring." With those three events, my knowledge was exhausted for rioting or uprisings in 1968.

Good luck.