The Sport of Revenge

– The K Zone –

The Sport of Revenge, by Ian Joffe

August 23rd, 2018

We all know the story: a player gets traded or DFA’ed by their team, and they can’t stand it. They join another team and, in their frustration with their old team or themselves or just the world in general, they start crushing the ball. Suddenly, the old unrosterable player is the player of the week and the month, until they eventually cool down. After that they may return to who they used to be, or be slightly better, until they come back to face their former team. As a Red Sox fan, I always remember David Ortiz punishing the Twins, especially in Minnesota. It seems like every team has players like that, but just because a few players crush their old teams it doesn’t mean everyone does. To answer that question, it’s going to require a look at a lot more players.

There are multiple reasons why a player would do better against their old team. The most simple reason is the psychological effect. I think that traditional sabermetrics (which would argue players do not do better against their former teams) often overlooks the science of psychology in places where data shows there could be a trend (for example, closers pitching poorly before the ninth). Players may feel angry or that they have something to prove to the club that abandoned them, and that could somehow affect their performance on their field. Additionally, they may have extra non-public knowledge about the pitchers on the team that they’re now facing. The same would apply in the inverse with the pitchers knowing more about the hitter in question, but because hitters tend to improve during in-game at bats against a pitcher as the innings pass by, it’s possible that hitters will have the advantage in this team-switch case as well. Third, there could be a park factor, where players are more comfortable in a ballpark that they used to play in, or fans motivate them by cheering or booing. That third reason is probably the least likely, as it only applies in the away ballpark and there’s little proof that fan interaction has a psychological effect, but it’s worth noting.

Since 2000, batters in MLB have had 107,790 plate appearances against teams they used to be on (I’m not sure, but I think that should be a large enough sample). Using a Python program to compile Fangraphs data, I compared how players did in those “Revenge PA’s” compared to normal plate appearances. Here are the results:

	Average Player	Players vs. Former Teams
AVG	.260	.258
HR%	2.7%	2.8%
K%	18.5%	18.4%
BB%	8.4%	8.7%
wOBA	.323	.324

 

In part due to the large sample, there is almost zero difference between the everyday player and players against their former teams. From this study, the simple, albeit disappointing conclusion is that the average player is no better against a club that they used to play on.

An interesting side note here from the study itself is the question of why I (and I assume many readers) had the misconception that many or most players will do better against their former teams. When players do well against their old teams, it creates drama which compels media to cover it, and the media covers it because they think people will be attracted to the apparent drama. And, they’re right. I wrote a whole article about this because it interested me. My point is that we have this misconception because the media over-covers stories that seem dramatic. They would be less likely to cover, say, Mookie Betts hitting .350 against the Giants because he’s never played for San Francisco, so there’s no drama there. We need to be aware of biases in what the media covers like this one and make sure that we realize that these stories about a few players that get covered for dramatic reasons do not necessarily reflect on everyone in the average population pool; whether that be baseball players or people in general. But I digress…

Having concluded that the average, aggregate player may not experience a change, I wanted to look into individual players. After all, everyone is affected differently by psychological factors and there may still be an abnormally high amount of players who perform well against their former teams. So, filtering out players with less than 20 plate appearances, I checked how many players hit .400 against their old teams – there were only 11. Then I looked at how many hit .350 – only 30. That’s a lot of players to reach those totals in a full season, but in the very small samples that I’m looking at, those numbers are very normal. They could be explained purely through luck in statistics, without psychology. Still, I wanted to see if there was any way I could show a real physiological difference for those few players.

Theoretically, if random streaks explain why these few players improved against their former teams, the increase in batting average would be independent of other statistical changes. A change in batting average would lead to a small change in other stats directly (for example, if BA goes up by .010, out rate will go down .010), but if there consistently are other effects than that, it can be shown that there is something unusual going on. In other words, if more than one statistic is drastically changing, this may not just be randomness and luck playing out. In order to look at a few different samples, I made three groups:

“The 30” are the 30 players who hit .350 in at least 20 PA’s

“The 11” are the 11 players who hit .400 in at least 20 PA’s

“The 5” are the 5 players who hit .350 in at least 60 PA’s

Here’s the data on a few stats from each group:

	The 30	The 11	The 5
HR%	4.3%	4.6%	6.7%
K%	14.4%	14.2%	11.9%
BB%	8.6%	7.1%	10.1%

 

Comparing these numbers to the league averages you can see in the earlier table, there are clear changes. Even after factoring in the direct changes (the pure change in batting average for The 30 and The 11 should put K Rate around 16%, for example), players improved significantly in power and in avoiding strikeouts. The only place that we don’t see a consistent story is in walks, which is weird but can probably be chalked up to the small samples that I’m dealing with. Looking just at strikeouts and home runs though, we can see clear improvements. That tells me that there could be more than randomness going on in the BA improvements for these players. It looks like they actually are motivated to be better against their former teams. Furthermore, the decrease in strikeouts tells us that there is no conscious change in approach. None of the groups are more aggressive at the plate, which would lead to an increase in strikeouts and consistent decrease in walks. This leads me to believe that the change is less conscious and harder to explain in baseball language (such as “more aggressive” or “faster swings”) – it’s more purely psychological.

In the end, the results of this study are that revenge psychology factors little into the performance of major leaguers. Very few players are better against their former team than any other team. There are, however, a very small select group of players who seem to be legitimately better against their former teams, but it’s hard to explain exactly what they do differently. When asked about his performance against the Mets, Daniel Murphy, one of The Five and the subject of one of the first K Zone articles said “I don’t know. They’re a division rival.” There’s little information from other players. While some may not want to openly admit their feelings on the subject of their old team, for the most part it seems that these players are not particularly conscious of their performance at all, at least while it’s happening. This is more the work of deeper psychological effects in a small portion of the population. Perhaps one day we will have neurological information on draftees or free agents so that teams can predict if they will be an unconscious vengeance seeker. For now though, it’s safe to assume that a random player will not come back to bite.

Oh, and while I was writing this article this happened. We’ll see if Murphy goes on to terrorize the Nationals as a Cubbie.

Sources:
Fangraphs
The New York Post

Images Attributed to:
USA Today

If you liked this article, you may also be interested in this short piece about whether or not players hit any better on their birthdays. Or, you can follow The K Zone on Twitter and be the first to know when we publish research, interviews, or other great new content.

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