"Stampede of zebras", apparently, is a bio-ethics term. "If you hear hoofbeats, don't look for zebras." Meaning, be cautious about making surprising diagnoses. Oddly appropriate for a mafia game clue.
Or that meaning might be completely unintended. It's short enough to suggest that it's false, so I shall ignore it.
First thing that comes to mind when I see 'rating chart' is the scoreboard in Zack's Sith Lords game, which is headed by electric926. Since I'm ignoring the first clue, may as well put a second vote on someone else on that chart: CivGeneral.