The "toughness" I'm talking about is playing the game with fire and emotion. And being willing to do anything and everything in your power to not lose. Some of the guys that come to mind had really good statistics, so let me name some that were good players without gaudy numbers that come to mind.
Ryan Gill was a tough AF ball player. Remember him? I loved the way that kid played the game. More recently, Evan Powell and Joe Robbins and Kennon Fontenot were tough, hard nosed players. Hunter Kasuls is tough. I'll add that I think Daniel Lahare is tough and plays the game the right way. I see a lot of it in Orynn Veillon too, and Lahare and Veillon are private school guys.