Are minority groups affected largely by individual acts of racism or by institutional acts of racism?

Racism remains to be a pervasive issue in the United States. Consider how American society has (or, has not) addressed racism over the years. Has racism improved in the United States over the years or has racism shape-shifted the variety of racially violent experiences people of color may experience?
Are minority groups affected largely by individual acts of racism or by institutional acts of racism? Are racist acts mostly overt or subtle, microaggressions? Please use examples to support your claim.