Roll-back - Change of rating deltas for each contestant who participated in a particular contest. In general, it occurs after the plagiarism check.
I have been seeing noticeable plagiarism checks for all the contests. However, the rating roll-back is not noticeable for all the users. Additionally, I came across several blogs discussing the indistinguishable change even after roll-backs, delayed roll-backs, and dissatisfaction with the roll-backs.
So, here is a request to @admin to pop a notification before a rating roll-back to avoid unnecessary speculation and transparency of roll-backs.