"mean_diff" represents the mean change in standardized OPR coefficients (mean across all teams at the event) after the corresponding match "ppt" (plays per team) is the number of match plays the event has had, divided by the number of teams at the event. So for example after 2025mdsev ran match 13, there had been (13 * 6 = ) 78 "plays", across 28 teams at the event, for about 2.79 ppt.