Hi,
Unfortunately it is not possible to reset the score without deleting the previous matches. The calculation method will recalculate all matches after you reset the score.
It is possible though to make a ranking of just a subset of matches. That way you can group certain matches in one match round and only calculate the ranking based on those matches. In a way that is also a way of resetting the scores because once you enter the match round for the new matches, everyone starts at 0 points.
A disadvantage of the custom rankings is that the calculation can take a long time if you do a full calculation, because it recalculates every ranking separately and also a ranking for all matches. But when a match round is finished and the final score for that ranking is calculated you have an option to disable (re)calculation of the ranking.
The easiest way to make custom rankings, is to group matches in a match type and add these match types to the ranking. See the Admin ? Rankings page for details.
The help page in the admin also has some information on the rankings. And how to use them with shortcodes if you want to display just the ranking for a certain match round.
HTH.
