### The MLB Rule Change

Although I am traveling in a country that does not fully appreciate baseball, I thought it would be fun to briefly explore the patterns of intentional walks in baseball history. As most of you know, MLB recently decided on a rule change. Teams no longer have to throw four balls to give an intentional walk — they simply indicate (maybe by showing four fingers?) that they want to give an intentional walk and the batter can go to first base. This rule was made supposedly to speed up the game. But this is really silly, since so few intentional walks are given per game — this will have a tiny effect on the length of a game. MLB needs to make a more serious effort if they really want to significantly shorten the length of games.

But this rule change made me wonder about the intentional walk strategy.

- Are teams using this strategy more or less than in the past?
- Of the batters who get intentional walks, how many intentional walks do they get per season?
- How many intentional walks are given to the IW leaders?

I’ll use graphs to answer these questions.

### Data

I’ll use Retrosheet play-by-play data for the 1980 through 2016 seasons. The key variable is EVENT_CD; a value of 15 indicates an intentional walk.

### Count and Rates of Intentional Walks

First I found the number of intentional walks given per season and constructed a graph of these counts. Generally, we see an increase in intentional walks from 1960 to 1970, a steady number until 1990, a dip in the 1990’s, an increase, and then small numbers in the last five seasons.

I can construct a more useful graph by adjusting these counts by the number of PA’s. Below I have constructed a graph of the rates of intentional walks Intentional Walks / PA over time. This gives a different pattern. Actually, the highest rate of IW was in the late 1960’s and there has been a downward trend in the rates. Currently, the rate of intentional walks is only about 0.005. (The dip in the rate during the Steroids area is interesting.)

Of course, intentional walks are not given to all batters. Of the batters who do get intentional walks, how many IW do they get, on average? Here’s a graph of this average across time. This mean number has shown a bit of variability across seasons — currently the players who get intentional walks get about 3 of them on average.

Of course, a post about intentional walks has to mention some of the great IW accomplishments. Instead of the mean number, suppose I graph the leading number of intentional walks achieved by a single players for all seasons.

Generally, the leader gets about 25-30 intentional walks in a season, but there were a few remarkable seasons where the leader got over 50 walks. In fact, a single player got over 100 intentional walks in the 2004 season. (If you don’t know the identity of this player, do some research on the Steroids Era of baseball.)

### Future Explorations

I encourage folks to investigate this intentional walk strategy further. Here are some questions to get you started.

- Intentional walks occur during which runner and outs situations? (I would suspect that IW’s typically happen when first base is open, such as runners on 2nd and 3rd.)
- What are the inning effects? (I am guessing that intentional walks are more likely to happen in the later innings.)
- Are there specific teams that tend to like or not like to use intentional walks?
- Are IW’s more likely be used later in the season?

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