That's an oxford comma. If your job is to proof read university papers and you completed a highest level university course in grammar, you should of recognised that. Now stop getting so triggered by everyone.

It is an Oxford comma; I'm saying that you used one too many. It should be "cautious, skilled players." It shouldn't be "cautious, skilled, players." When you put it like that, you're separating your adjectives from the noun you're describing. In this case, the noun is "players." You wouldn't say "Those are some skilled, players." You would take out the comma. When you're listing more than one adjective, you do have to use commas for listing purposes, but the last adjective describing the noun never has a comma after it.