Baseball Prospectus provides fans with the look at the most innovative metrics in baseball, ranging from true average, to deserved run average, to pitch framing, and now, they even have pitch tunneling data. They provide great ways to analyze and digest the game, and as sabermetrics have grown into the mainstream over the years, Baseball Prospectus has increasingly been a point of reference to me.
Because of the mass amount of research done by their stats team and writers, we have data that can match what we see, or go against our eye test and prove us wrong.