The Crazies was a remake of a 1973 film by George Romeo. He was actually the executive producer for this movie, which is much better than the original.
A military plane with a mysterious agent crashes near a town in Iowa and slowly infects everyone. The agent makes people violently attack others. The first hint something is wrong is when a man wonders onto a field during a baseball game with a shotgun and local sheriff David (Timothy Olyphant) has to shoot him. Things quickly escalate as the army is sent in to cleanse the town.
Romero of course was made famous by his series of zombie movies. This was a variation of that theme where average middle America faces a sudden mass catastrophe by being infected with deadly consequences.
Romero’s original was a low budget grindhouse film. This one did a much better job with all the elements. The tension is greater as the virus spreads. The horror of what people do when they join “the crazies” is much more shocking. The government turns out to be a sinister force rather than a helpful one. Overall, things are a lot scarier with this newer version than the original.