Unfortunately, the information is too poor to start investigating.
Could you share your workbook or sample data as packaged workbook (**.twbx) ?
As Shin, we really need more information and preferably a workbook to help us help you. Saying this, a simple Moving Average calculation will help you and you are on the right lines with using a table calc to attempt this though the Window_Avg() table-calc is your friend here
If we knew how you are defining a 'match' then we would be better placed to provide this calculation as it sounds as though your calc hangs-on knowing the number of matches to rll-over.
As a basic example of a seven-day rolling average: Window_Avg(Sum([Sales]),-6,0)
The issue we currently face is knowing the calc behind the "-6" in the calc or in your case, "-2" - you have said it currently needs to go back 3 but as the starting position is base 0, we need to factor the -3 down by 1 to -2.