For hitters, for years and years, it was batting average that was thought to be the best single statistic to look at to evaluate a hitter. In the last couple of decades, the weaknesses of batting average have been exposed and the value of getting on base and hitting for power have become better recognized. The stat that is becoming the new standard for hitters is OPS—On-base percentage Plus Slugging percentage.
For pitchers, the standard is ERA. Compared to batting average, it provides a much better representation of effectiveness. It measures the most important quality of a pitcher's job, preventing runs. However, it too has its flaws. The biggest flaw is that a pitcher's ERA can be greatly affected by the pitchers that immediately follow him in a game, both positively and negatively.
Enter Opponent OPS. This is a stat that you hardly ever see. It makes just as much sense to look at Opponent OPS for pitchers as it does to look at a hitter's own OPS. We just recently added this as a leaderboard titled "Opponent OPS" to Bill James Online and I wanted to share it with you.
ERA is going to continue to be the standard, and I will personally look at ERA for every pitcher, but I think Opponent OPS may be a better indicator of a pitcher's overall effectiveness. In fact, in a way, we've been suggesting this for quite a while as we've published component ERA in the Bill James Handbook. Component ERA is, in essence, a restated Opponent OPS since it is based on nearly the exact same components that go into OPS, namely hits, home runs, walks allowed, and hit batsmen. Opponent OPS adds in doubles and triples allowed as part of the equation.
Here are the Opponent OPS leaders thus far this year:
| Opponent OPS—2008 |
| Player | OPS | ERA |
| Ryan Dempster, Cubs | .561 | 2.75 |
| Edinson Volquez, Reds | .563 | 1.32 |
| Brandon Webb, Diamondbacks | .567 | 2.69 |
| Shaun Marcum, Blue Jays | .568 | 2.63 |
| Jose Contreras, White Sox | .570 | 2.89 |
| Ervin Santana, Angels | .592 | 3.02 |
| Cliff Lee, Indians | .603 | 2.45 |
| Roy Halladay, Blue Jays | .609 | 2.94 |
| Joe Saunders, Angels | .614 | 2.63 |
| Tim Lincecum, Giants | .624 | 2.23 |
The number one guy so far this year is a surprise, the Cubs' Ryan Dempster. Dempster struggled as a starter and did well as a reliever earlier in his career. Now he is turning it around and doing great as a starter after having some relief problems late last year.