What if, during violent clashes with police, two of the protestors die from heart attacks. Would that count for the purposes of this market?

@EMcNeill Good question! First of all, note that the description says "more than 2".

If 3 people had heart attacks and died, I think I'd resolve that as "yes". Dying is a pretty unusual outcome -- if 3 people die in one incident, it's probably not a pure coincidence. (And if it was pure coincidence, well, that's the way predictions go sometimes.)

@PeterF I don't want to put myself in the situation of deciding what the causal factors were in each death.

Note though that the deaths have to occur during confrontations with authorities. (Or from injuries sustained in those confrontations.) If people are peacefully protesting during the day, and then at night the cops start tear gassing the crowds, a heart attack during the daytime peaceful period doesn't count. (I'll have a low bar for what counts as "confrontation" though.)

You say "not subsequent deaths while in custody". What about deaths in custody that are due to injuries incurred during? Or rather, that are alleged to be due to such injuries, or partially due to them.