This is easily avoided by joining the two strings with some character or character sequence that (you hope!) cannot possibly occur in team or player names

Or, take the guesswork out of it and add an extra layer of depth to the hash:

    unless $seen{$team}{$player}++;
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Another, possibly more significant nit. All team and player name data in the OPed example is uppercase. If there may be any mixing of case ...

True, but to be fair to the OP it was stated to be just an example. I'm not convinced that dirtdog is actually applying this to teams and players. If he were then he would have bigger problems with real-world data such as the current All Blacks XV which has featured all three Barretts in recent weeks. You can't go de-duplicating three different players who share the same surname.