How important are batter/pitcher matchups? (Part 2)

July 12 11:27am
Derek Carty

Last week, I examined one of the most common myths of daily fantasy baseball: batter/pitcher matchups. To be more specific, last week I examined whether a batter’s history versus a particular pitcher was indicative of how he would perform the next time he faced that pitcher. My findings showed that they were not, which, when you really think about it, makes sense. After all, with the thousands of at-bats we have to tell us how good a batter is, a few against a certain pitcher shouldn’t tell us nearly as much. Today, I’m going to look at the reverse and see whether a pitcher’s history against a particular batter is of any use to fantasy league owners.

The Study

For my study, I’m going to be looking at all single day batter/pitcher matchups since 2000 where the pitcher faced the batter at least two times. For every matchup, I’m going to first compare the pitcher’s career numbers against the batter to how he performed against the batter that day. Then, I’m going to compare his preseason Marcel projection (thanks as always to Jeff Sackmann for his historical Marcels database) to how he performed against the batter that day. This will tell us which is better to use – the pitcher’s career against the batter or a simple projection, ignoring the pitcher entirely. When comparing these sets of numbers, I’ll be using average error to study the differences.

I’ll further break things down based upon how many times the pitcher has faced the batter in his career. After all, while few will argue that allowing a 1-for-3 batting average against lifetime against a hitter is meaningful, some will be satisfied with 4-for-12. Others will still say that’s too small a sample but that 7-for-21 is sufficient. Where we draw the line is a subjective distinction that everyone has their own opinion about, so I’ll look at every sample size of career plate appearances to see how many is needed, if that point ever comes.

The Results

Here are the results for pitchers facing hitters. I’ve had to limit the stats I look at because things like wins and earned runs aren’t attributable to a matchup with a single batter. Instead, I’ve looked at batting average and on-base percentage against, as well as wOBA against. I’m not looking at FanDuel points because wins and earned runs make up a large portion of FanDuel points, but it’s impossible to examine them in this context.

I should also note that Jeff’s historical Marcels don’t project batters faced for a pitcher, so I had to estimate it using IP*3+BB+HBP+H, which is far from ideal. It also leaves out ROE, which is a part of wOBA. Additionally, it only projects hits and home runs, so for singles, doubles, and triples, I broke down (H-HR) based upon league average rates. Combine all of this, and Marcel wOBA is going to be handicapped quite a bit. Keep that in mind.

In the table below, the first column gives the number of career plate appearances the hitter has had against the pitcher in his career. The second column gives the number of batter/pitcher matchups I’m drawing from. The next three columns give us the difference between the average error for the projection and the average error for the career vs. pitcher. A green highlight means that the projection is better while a red highlight means that the career vs. pitcher data is better. So for batters with between 1 and 5 career plate appearances against a pitcher, the career vs. pitcher data will be wrong by 0.054 more than the projection will (on average).

To give a very simplified example, if a pitcher actually allows a batter to hit .250 on a given day, the projection might say that he should hit .270 while the career data might say he should hit .324. Both will be wrong to an extent – after all, we can never guess a player’s performance perfectly – but the career vs. batter data will be wrong by 0.054 more than the projection will.

Well, this is interesting. For batting average, the projection is better up until 30 times against a hitter but remains slightly better or roughly equal up until 100 times.

OBP and wOBA, though, are quite different. For the lower samples, the projection is easily better than the career data. Once a pitcher has faced a batter 20 or 25 times, however, his history against the batter becomes just as good as the projection. After that, the career data becomes slightly better the more career matchups but never overwhelming so.

Final Results

Overall, it appears that the projection is far superior to a pitcher’s career versus a hitter, at least until they’ve faced each other a couple dozen times. After that, the career data appears to become slightly better, but I would be wary of this finding for many reasons:

1. The projections I’m using are Marcels, which are the simplest of projections
2. The projections are from before the season. Once we actually get into the season, that projection is going to become less and less accurate, especially when we’re looking at matchups that occur in, say, August.
3. The career versus pitcher data contains at-bats from the current season; the projection ignores the current season entirely
4. All of the limitations of what Jeff’s Marcels actually project that I mentioned earlier, namely the exclusion of batters faced, singles, doubles, triples, and reaches on error.

Additionally, it’s important to note that platoon splits are much greater for pitchers than they are for hitters since pitchers can choose to throw a variety of pitches that may be better suited for either a lefty or righty batter and can throw from a variety of arm angles (in general, the lower the angle, the greater the split).

Given all this, I still believe that it would be prudent to trust a quality in-season projection and thorough analysis to a pitcher’s career versus a particular batter, especially if that projection or analysis takes platoon splits into account.

While it’s likely that some pitchers do hold some special qualities that allow them to dominate a particular hitter, or simply have a certain hitter figured out, it’s very difficult for us to identify these pitchers by merely looking at the raw data.

There are, however, certain batter/pitcher matchup considerations that we can give credence to, such as platoon splits (as already mentioned) and the possibility that certain pitchers perform better against certain classes of hitters.

Concluding Thoughts

That wraps it up for this week. As always, if you have any questions, feel free to comment or e-mail me. Also, be sure to add me as a friend on Facebook and follow me on Twitter.

Derek Carty’s work can also be found at Baseball Prospectus, CardRunners Fantasy Baseball, and He has previously had his work published by The Hardball Times, NBC’s Rotoworld, Sports Illustrated, FOX Sports, and USA Today. He is the youngest champion in the history of LABR, the longest-running experts league in existence, and is a graduate of the MLB Scouting Bureau’s Scout Development Program (aka Scout School). He welcomes questions via e-mail, Facebook, or Twitter.

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