ShaunMcClarty:i dont know how exactly they get it but its not and exact scoring average
10 best out of your last 14 scores. More recent scores weighted more heavily.
Everytime you post a score, one drops. If what drops off is higher than what you shot, chances are the average will go down.
It's quite common to shoot higher than your average and drop your average. It's equally as common to do the exact opposite.