Pitching Performance Value

How do you truly identify how well a pitcher performed? Looking at his ERA+, WHIP or his K/9 rate may be misleading. What if a set up man comes into the game and gets out 3 great hitters and then the closer comes in and gets out 3 mediocre hitters. Their performances look the same on paper, but they actually aren't. The set up man had to work harder to get the outs and those outs held more significance.

I would like to establish a statistic that shows this. This one is very simple: it is just a ratio of ERA to the average OPS of the hitters faced. It will look something like this: PPV = ERA/ AOPS.

On September 25, 2011 The Yankees played The Red Sox in a double header they lost in extra innings in one game and won the other. In the first game David Robertson pitched four outs and faced David Ortiz, Jacoby Ellsbury, Carl Crawford, Adrian Gonzalez and Dustin Pedroia. He struck out Ellsbury, Ortiz, Gonzalez and Crawford flew out. Mariano Rivera pitched in the second game and he faced Jarrod Saltalamacchia, JD Drew, Marco Scutaro, Mike Aviles, and Adrian Gonzalez.   He got out Saltalamacchia, Drew and Aviles.

I chose September 25, 2011 because it was close to the end of the season and their stats were close to complete. The OPS of the opposing players should be taken on the day of the performance, because hot and cold streaks do exist. Although some people believe hot and cold streaks do not exist, they do. You need to know how well the batter was doing up to that day. A batter could hit 5 home runs in one week and then 0 for an entire month.

So Robertson got out Ellsbury (.928 OPS), Ortiz (.953 OPS), Gonzalez (.957 OPS), and Crawford (.694 OPS). Robertsons ERA was 1.08. So the stat would be set up as PPV = 1.08 / ((.928 + .953 + .957 + .694) / 4). That turns out to be 1.22. The lower the number the better. Marinao River had an ERA of 1.91 and he got out Saltalamacchia (.737 OPS), Drew (.617 OPS), and Aviles (.775 OPS). 1.91 / ((.737 + .617 + .775) / 3) =  2.69

Robertson performed better than Rivera on September 25, 2011.  I know they didn't pitch in the same game, but the batters they faced are the main reason. You can use this stat to evaluate a pitchers performance on any day, as long as you use the batters OPS for that day. It also works for starting pitchers, but there will be a lot more numbers to average.