Cool, thanks @blanchy (and @talesfrmthecrypt).
This part made me think of another question...
A player who stays in the PL but stops playing is different: missed matches don't count as zeroes
I assume that sub appearances count... so a player who comes off the bench and scores 1 point (or comes off the bench, gets booked and scores 0) contributes towards the last 4 appearances. i.e. we're not looking at just "last 4 starts".
Yes that's right. Any appearance counts towards the average score so it's the average score of the last 4 appearances (whether starts or not)