Protection is just one of those things in baseball that is largely believed to exist. Having a good batter behind you in the line-up can help you and a poor batter can hurt you. Now, though protection is part of the conventional baseball wisdom, the sabermetric community seems to be a little more skeptical. Here is a sample of some of the studies I know of.
David Marasco has a nice little write-up on protection in The Protection Mini-FAQ.
In the 1985 Baseball Abstract, Bill James used a case study of Dale Murphy and Bob “I’m tired” Horner. Horner’s great playing shape provided an excellent natural experiment during the 1984 season. Murphy, who batted in front of Horner, hit better with Horner in than Horner out, but the difference was not statistically different. The Grabiner study below has a brief summary of James experiment.
David Grabiner looks at 25 players from the 1991 AL who bat have many at-bats with and without a slugger on-deck. He found no evidence that a better on-deck batter helped the preceding hitter.
Dylan Wright uses a method similar to Grabiner’s for the 2002 NL. For his “protectors” and “protectees” he finds mixed results.
In general, these studies used matched pairs of hitters that reflect when we think protection should be happening. Mainly, we have two good hitters next to each other in the batting order. While this is one way to do it, I think the search for natural experiments in matched pairs unnecessarily limits the sample size. As an economist, I see “protection” as an externality. That is, the contributions of one player are spilling over onto another player to generate harm or benefit. It helps to have Barry Bonds bat behind you, it hurts to have Neifi Perez. If protection exists, I view it as a continuous concept that applies to all players. Bad players hurt preceding hitters, while good players help them. And the degree of ability affects the amount of the spillover. Why not look at the impact of the quality of the on-deck hitter to see if he is impacting the current hitter in all situations?
So, I did…or more correctly, Doug Drinen and I did. We’d been discussing the concept of protection for a while, but this summer we finally broke down and did something about it with play-by-play data. Using Retrosheet event files we were able to estimate the impact of every on-deck hitter on the current hitter from 1984-1992. The play-by-play data allowed us to control for the game situation during every plate appearance. While we were looking at protection, we were also curious in identifying another possible spillover, which we call the effort externality. While having a good hitter batting behind you might put more balls in the strike-zone, it doesn’t mean these pitches are of the same quality than with a poor hitter on-deck. It’s not that the pitcher just wants to avoid walking a batter when a good hitter follows. The pitcher wants to keep the hitter off-base any way he can. Pitchers are not dumb. They understand that putting more balls in the strike-zone increases the chance that the hitter will reach base via a hit, possibly with power. So, pitchers may reach back for a little extra gas in these situations. This means that a good on-deck hitter has reason to lower a current batter’s chances of reaching base via a walk AND a hit. If the effort effect is larger than the protection effect, then a good on-deck hitter can hurt rather than help the batter in front of him. Since the effect is ambiguous we need to go to the data.
The results lead us to not only reject the protection hypothesis, but also we find evidence that good on-deck hitters actually harm the hit and power probabilities of the current batter. This is consistent with the effort hypothesis. However, the magnitude of the spillover is tiny and for all practical purposes the effect is zero. Even very good (bad) hitters have only a very small impact on the batters who precede them.
“But what about [insert possible excluded variable]?” Well, we controlled for a heck of lot of potential outside influences: platoon effects of the batter and the on-deck batter, the base/out configuration, the quality of the pitcher, the score differential, the inning of the game, and the park in which the game was played. Given the number of observations we are convinced that protection is a myth; it doesn’t exist.
If you want to read the study you can find it here. It is full of Greek symbols and confusing terminology (it’s written for an audience of academic asshats), but you can largely skip over most of this to get the big picture. Enjoy!