Formula's are well and good, as are explanations of what the stats mean, but what's the reasoning behind that formula? basically i think it's an effort to give people one super-stat that measures a player's offensive contributions - it includes baserunning as well. a lot of people think OPS+ is supposed to be that stat, but because of how slugging is defined - most of the time a guy is going to have a higher SLG than a OBP. assuming baserunning is basically equal, a player whose OPS is .800, with a .400 OBP and .400 SLG, is easily more valuable than a player with a .300 OBP and .500 SLG, even though their OPS's are equal. anyway, back on EqA. i think clay davenport created it with the intention that fans who are used to batting average can understand it more easily. an EqA of .260 is league average, and this is generally pretty true for batting average as well. so if a guy has a .350 EqA, he's really awesome, and if he has a .190 EqA, he's really atrocious. it's a pretty awesome stat, and probably my favorite "common" offensive stat to use.