Defensive Shifts and Ground Ball Batting Averages


A few years ago, I introduced the new shifting data available in Baseball Savant and illustrated some basic exploration on shifting. As we know, infield shifting is currently prevalent in MLB baseball, although I am not sure we understand the total impact of defensive positioning on offense. In this post, I’ll use the 2019 Statcast data to explore the current infield shifting patterns of the 30 MLB teams. One main purpose of infield repositioning is to prevent ground balls from being base hits. So we’ll focus on batting average on ground balls and explore how this batting average depends on the batter side, the direction of the batted ball (in the pull or opposite sides of the field), and the defensive positioning. We’ll provide a brief justification of shifting and show some interesting differences and similarities how teams approach right and left-handed batters.

Shifting Rates of the Teams

In the Statcast dataset, there is a variable if_fielding_alignment that indicates the fielding positioning for each pitch. Using the 2019 data, I collected the fielding positioning for the last pitch of each batter and, for each team, found the percentage of shifts for all left-handed hitters and the percentage of shifts for all right-handed hitters. A scatterplot of these percentages is shown below and the red line indicates where the “left” and “right” percentages are equal. Several interesting comments from this graph:

  • Teams tend to shift more often for left-handed hitters. Minnesota is the only team who shifts against left and right-handed hitters the same rate. Toronto is more typical — they shifted about 45% of the time against left-handed hitters and only 15% against righties.
  • There is a remarkable variation between the teams on their shifting rates. The LA Dodgers have high rates of shifting for all hitters. Boston, in contrast, almost never shifted against righties and shifted about half the time against lefties. Cleveland appears to rarely shift against hitters on either side.
  • The shifting variability that we see indicates that teams may have different philosophies about the value of shifting. I may have thought that teams might be more similar since they have access to the same data and much of the research on the value of shifting.

We’re going to focus on hits on ground balls, so the following graph displays the allowed BA on grounders from hitters on both sides. The LA Dodgers are the stingiest team in the sense that their allowed BA on groundballs is smallest against lefties and righties. In contrast, Detroit and Texas allow high BA’s against both types of hitters. Of course, defense positioning is only one variable relevant to BA. A team also needs infielders with good range to field ground balls in the holes. This graph indicates that teams vary quite a bit on this defensive statistic since batting averages of 0.24 and 0.32 are quite different.

Batting Averages on Grounders

Let’s focus on players’ batting average on grounders. First we compute the BA for left and right-sided batters when they hit in the pull and opposite side directions. As one would expect, players hit for a higher BA when they hit to the opposite side, although the difference between the BA for grounders hit in the opposite and pull directions is much more pronounced for left-sided hitters.

Infield positioning plays a large role in the player’s BA on a ground ball. Below I show the ground ball BA for both batting sides against different fielding alignments (shift, standard, or strategic). Clearly, the shift alignment appears to result in a large drop in the batting average and the size of the drop seems greater for left-sided hitters.

The next graph shows how the ground ball BA depends on the batter side, the hit direction (opposite or pull), and the field positioning. For example, the effect of an infield shift drops the BA of a leftie under 0.200 on balls hit to the pull side. But the shift has the effect of increasing the BA of a leftie over .500 to balls hit to the opposite side. Similar effects happen to right-sided hitters — shifts do well in preventing pulled ground balls from becoming hits at the expense of making it easier to get singles on opposite side ground balls.

Of course, teams know which players tend to pull their ground balls. Below I show the percentage of pulled grounders for each batting side and each possible fielding alignment. As expected, the “shifted” batters are much more likely to pull their balls than the batters getting a standard fielding positioning.

Looking Deeper at Team Infield Defense

We saw earlier that teams differ substantially on their shifting strategy. Can we detect the differences between teams by taking a closer look at their abilities to prevent hits on ground balls?

Let’s focus on balls hit to the pull side. For a right-handed hitter, we can round the spray angles in the pull side to the values of -45, -44, …, -1 degrees where 0 degrees is up the middle. For each team and each degree value, I compute the fraction of ground balls that are hits and plot a smooth of the hit fractions as a function of the angle. This graph below is what I get. What is remarkable about these 30 plots is the similarity in the appearance. For most teams, a hitter can generally get hits at the -5 and -25 degree positions for all teams. What this tells me is that teams tend to have similar infield alignments against right-handed hitters.

Let’s do a similar thing for left-hand batters who hit ground balls to the pull side. I divide the spray angles to the values 1, 2, …, 45 degrees and plot a smooth of the batting averages against the angle for all 30 teams. Here the graphs are not similar. For example, the curves for three good fielding teams who shift a lot (LA, HOU, BAL) are quite different in shape than the curves for three teams (CLE, COL, CWS) who don’t shift as much. What this tells me is that teams really differ on how they defend left-handed hitters. Teams like LA really seem to defend well against lefties to the pull side and other teams like PHI or CWS have patterns similar to what you see for right-handed hitters to the pull side.

Is it Worthwhile to Shift?

Teams are gambling when they shift. They are hoping that the batter will pull the ground ball in the area where they have an extra fielder. But the batter has a better chance of getting a hit when the ground ball is hit to the opposite side. Is it a good bet for the defense?

This table gives the BIP and BA for left-handed hitters under different strategies and different hitting sides. This information is helpful for answering the question (the same logic works for right-handed hitters).

  • When a shift is employed, the opposite side BA on ground balls is 0.549 compared with 0.345 with Standard fielding.
  • Since shift fielding is used for 2048 BIP, the batters gain 2048 (0.549 – 0.345) = 418 additional hits from the shift.
  • But on the pull side, the hitter’s BA is 0.155 on the shift compared with 0.260 with standard fielding.
  • Since shift fielding was used for 6785 BIP, batters lose 6785 (.260 – .155) = 712 hits from the shift.
  • So overall, the batters lose 712 – 418 = 294 hits with the shift which indicates that it is desirable defensive strategy.

Summing Up

Some interesting takeaways from this exploration.

  • Teams are very different in how they shift in the infield. I suppose teams have to work with the specific fielding talents of their infielders which may impact their defensive strategies.
  • Teams treat left-handed hitters differently from right-handed hitters. For example, teams shift much more against left-handed hitters although it seems there is value to shift more against right-handed hitters.
  • Looking at the BA against spray angle graph, there appears to be a standard fielding alignment for right-handed hitters that is used by all teams. In contrast, teams appear to have different strategies positioning against left-handed hitters.
  • I have only considered the impact of shifting on BA on grounders. Certainly the value of shifting is more than defending grounders and it would be interesting to explore other offensive measures that are impacted by shifting.


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