Formula to find averages in a table of a unique value

[mattbarbera]

Hi!
I'm trying to use a formula which can find the averages for a teams last score in the last 3,5,10 games. I've got an example of the table below and how it would look when I've got it working

https://docs.google.com/spreadsheets/d/1bY3PJSTGC2NSXMEVHxfaJFeYGJYoB47qursB9aQo07g

Would love to get some help with this, thanks!