The lagging moving average would be [-, 4.5, 3.5, 6, 6.5, 5.5, 8.5] as with a window of 2 it averages the current reading with the previous (making 2 readings) and the dash says we don't have enough data. I would have said the leading moving average was [4.5, 3.5, 6, 6.5, 5.5, 8.5,-] but the statement that lead must be less than or equal to lag gives me pause. From the Wikipedia page:
"For a number of applications it is advantageous to avoid the shifting induced by using only 'past' data. Hence a central moving average can be computed, using both 'past' and 'future' data. The 'future' data in this case are not predictions, but merely data obtained after the time at which the average is to be computed."
But I don't know why a leading average (as opposed to central) might not be of interest.