When you get a punching bag it is randomly decided what bag you will get. What is the chance that it will be a Reset Bag?
There is currently no known rate, and the exact rate will be unknown until the people who are currently working their way through the games code find it.
Reset bags are fairly uncommon however, if you assume that there is an equal rate of obtaining a bag:
6*3 (stats bags) + 8 special bags = 26 bag types
That's a 3.4% chance.