Right, Left, Side to Side: Horizontal Pitch Movement Frequencies

A couple of the interesting terms in baseball’s lexicon are “front door” and “back door” pitches. Front door pitches start inside on a hitter, but end up cutting across the inside portion of the plate. Back door pitches start off the plate outside —away from the batter— and bend back to cross the plate’s outside edge. This post is motivated by those terms and a curiosity to understand the relative frequencies that they occur, as well as other forms of side-to-side pitches more broadly.

Pretty simply, the goal here is to determine how often pitches are moving toward a hitter versus away from a hitter. As part of that, pitcher and batter handedness are taken into account. Adding a layer of complexity, it also considers the side of the plate those pitches are thrown on, in order to consider the front door or back door portion of things. The data that follows should therefore address a hypothetical question like, “how often do left-handed pitchers throw pitches inside, that are also breaking toward the plate (a front door pitch, bending toward the third base side of the plate) to left-handed hitters?”

A quick note on the data. It comes from Baseball Savant and includes pitch-level data from across this season; specifically, it includes all pitch data from the first 6 days of each calendar month from April through August. Data were pulled in this manner in order to get a selection of pitches from a wider stretch of the season. Altogether, 118,243 pitches were a part of this analysis.

Statcast exports include data for batter and pitcher handedness, the horizontal direction of the baseball (as measured by the pfx_x field), and location of the pitch. Given pitch side (1B side and 3B side, split right down the center of the plate), pitch direction (again 1B side, 3B side), batter handedness, and pitcher handedness, there were 16 varieties of pitch outcomes here. What follows are some visuals as well as a breakdown of relative permutation frequencies.

To start, left-handed pitchers versus left-handed hitter frequencies. The image below may look like some hotel room modern art, but it is in fact an attempt to depict these various scenarios.

Things here are visualized from a bird’s eye view; the pitcher’s mound is at the bottom of the visualization and home plate is at the top, bisected by a turquoise line. The larger turquoise circle represents the batter’s handedness and the smaller represents the pitcher’s. The lines connecting the pitcher’s dot (or handedness or release point?) to home plate represent the side of the plate the pitches arrived on as well as whether they are moving toward or away from the batter. The colors and thickness of those lines represent the frequency of those types of pitches; darker lines indicate greater frequency of offerings. In this first visual, the turquoise dots that indicate the pitcher and hitter are left handed, respectively.

Hopefully, aided by the explanation above, one can make some sense of these visuals. The accompanying tables should hopefully shed additional light on things. Here, we can see the for LHP/LHH matchups that plate side and pitch direction are roughly evenly distributed, with the exception of “front door” type pitches. Relatively rarely are left-handed pitchers pitching to same sided hitters on the inside with pitches that are breaking toward third base. Some conjecture as to why might be a hesitance to throw pitches that might leak out over the plate. Better to focus on the outer half with those types of pitches such that the movement of the baseball is carrying it even further from a left-handed hitter’s barrel.

Next, a look at left-handed pitchers and right-handed hitters.

Here, pitches are more unevenly distributed. Far and away the plate side and horizontal movement profile most employed by pitchers in this case are arm side movement pitches that land on the outer half of the plate to righties. Again, this checks out in that pitchers generally aim to avoid pitching into, or toward, a hitter’s barrel.

Next up, right-handed pitchers facing left-handed hitters.

Right-handed pitchers facing left-handed hitters is something of a similar story to the inverse case. Here too, lots of arm-side movement is employed, theoretically to keep the baseball from running away from a left-handed hitter’s barrel. Note too the raw number of pitches here; this type of face off is much more common than those with left-handed pitchers, due to their relative rarity. Front door pitches appear far more often in these situations than back door; roughly a quarter of the time RHPs are pitching in on lefties with arm-side movement.

Pitching to same side hitters as a right-handed pitcher looks very similar to that of lefties facing their same side opposition. If you compare that first, left versus left, data above to this chart immediately above you can see the similarities: a roughly even distribution of pitches with the exception of front door pitches, of which there are markedly fewer. In fact, of all 16 permutations, on a percentage basis, right-handed pitchers throw front door-type pitches to same-sided hitters with the lowest frequency, less than 10% of their offerings. Again, it’s not especially hard to assign at least some narrative to that infrequency; it is dangerous to pitch to a hitter inside with an offering that moves naturally back over the plate (and toward a hitter’s barrel).

To wrap things up, below is a table with all 16 permutations taken together. To add some additional interest, SwStr% and Whiff% have been included in order to juxtapose frequency of offerings to their effectiveness by those measures.

At the outset of this exercise, I may have assumed that left-handed and right-handed pitchers approached hitters with more variability, but when data are aggregated that does not seem to really be the case. Whether left-handed or right-handed, pitchers employ 3 of 4 pitch variations roughly equally to same-sided hitters, while using front door-type pitches considerably less.

Meanwhile, there is more variability when facing opposite-handed batters; there, pitchers prioritize pitches on the outside half that move away from the hitter at very similar frequencies – roughly 41% of the time. The three other outcomes appear with varied regularity between 13-27% of the time.

So, on the whole it seems front door pitches aren’t particularly popular in 2025 while pitching toward the outside of the plate while back door pitches are considerably more common. Interestingly, Whiff% and SwStr% suggest there may be some value in tweaking approaches overall. Of course, data here is aggregated and each pitcher is unique, but some SwStr% values suggest various types of pitches might be worth employing more often than they are currently called upon.