The Violation frequency summary shows a histogram of the violation frequencies of the upper- and lower-bound distance restraints.
It shows how many of the restraints are violated in none of the models (ie are not violated at all), how many are violated in 1 model, 2 models, and so on - up to the number of restraints violated in all the models.
The main options for the Violation frequency summary are:-
These options can be altered by editing the parameter file, procheck_nmr.prm, as described here.