You've hit one of the more critical limitations of what FileMaker can do to chart summarized data. You can only sort on a single field to get the groups that are then summarized to get your Y-Series of data. Sorting on two fields doesn't work. One work around is to concoct a calculation field that combines the data from your two sort fields into one value that groups and sorts them the way you want them for the chart and then use that calculation field to sort your records.
In your case, depending on whether you want to see them grouped first by year or first by team, you might try:
Team & Year
Year & Team
as your calculation field with "text" as your result type. (Use 4 digit years)
Yes this rings a bell with something I was looking into a while ago. Was sort of hoping that there may have been an ability to do such a thing added recently.
Will use your method although it is not as neat as I would have liked.