ORA takes any player and tells you the number of runs expected to score per game if every batter in the lineup was the given player. I call it ORA (or oERA) because it tells you the ERA of an average MLB pitcher if every batter was the given player.
ORA or (oERA) stands for Offensive (earned) Run Average. It is calculated with a computer program that I created. The program behind the ORA takes the players probability of a given player getting a single, double, triple, home run, or walk, and then simulates an innings result 1,000,000 times and then multiplies it by nine because there are 9 innings in a game. For a more in depth description go to the bottom of this page.
2015 list coming soon
2014 ORA top 97
Basically it says if this player were to bat the odds of him getting any result would be
Result X occurences
Plate Appearances
This makes sense, if a player has 50 doubles in 500 plate appearances you could assume that when he's up you have a 1/10 chance of seeing another double. So then you could find the odds of scoring a run by hitting two doubles in a row if every player in the lineup were this guy would be 1/10*1/10 = 1/100 per two plate appearances. You could try to calculate the odds of every way of scoring a run (or not scoring a run) in an inning, but there are literally an infinite number. This program instead says that this player will bat until he makes three outs and then to simply submit the resulting number of runs. It then repeats this over and over again until it has submitted 1 million inning results. Then the average number of runs simulated to score in those million innings multiplied by 9 is telling you the number of runs expected to score per game if every batter in the lineup were the given player.
Result X occurences
Plate Appearances
This makes sense, if a player has 50 doubles in 500 plate appearances you could assume that when he's up you have a 1/10 chance of seeing another double. So then you could find the odds of scoring a run by hitting two doubles in a row if every player in the lineup were this guy would be 1/10*1/10 = 1/100 per two plate appearances. You could try to calculate the odds of every way of scoring a run (or not scoring a run) in an inning, but there are literally an infinite number. This program instead says that this player will bat until he makes three outs and then to simply submit the resulting number of runs. It then repeats this over and over again until it has submitted 1 million inning results. Then the average number of runs simulated to score in those million innings multiplied by 9 is telling you the number of runs expected to score per game if every batter in the lineup were the given player.