Along_the_Wire You really have to have played the game to understand it fully, the tactics, the intricacies of the rules etc, as Amps I think has said.
I haven’t played at a high level, but I played until 18, for both my school team (union) and a local rugby union side, and went to watch league frequently.
Union is much more complicated and fans who go but never played can also know the rule book but not know why a player makes a particular decision at a particular time.