Batted-Ball Trajectory: Splitting the Difference

One of the most familiar tactics in baseball is the handedness platoon. Nearly every adult fan knows that a pitcher does better against batters with the same handedness, and batters fare better against pitchers of the opposite handedness. Managers set their lineups to exploit this advantage, and in the late innings of a tight game will often burn through their benches and bullpens seeking an edge for as little as one plate appearance.

Not as well known is another kind of platoon. Players can produce a preponderance of types of batted balls that they hit or allow, between ground balls and fly balls. The proclivity tends to stick: you can be a groundball pitcher, a flyball hitter, and so forth.

In The Book, Tango, Lichtman and Dolphin examined the splits of the trajectory platoon, as I will call it. They found that when one type of batter faces one type of pitcher, the rules of the handedness platoon carry over. The batter would rather see his opposite type than one of his own style. (The pitcher wants to see a ground-ball batter because grounders do that much less damage. However, between batters with identical wOBAs, the pitcher would definitely prefer his own trajectory type.)

The trajectory platoon is not as dominant as the handedness one, mainly because it’s a continuum from one extreme to another. Batters and pitchers perform either lefty or righty: not even switch-hitters can hit 60 percent lefty in a particular at-bat*. It is a real effect, though, one that appears not to be exploited by managers in the same way. Although … perhaps the next time we’re decrying a weird pinch-hitting or bullpen move, we might look at it from this angle to see if the manager’s thinking on another level.

*Technically this may not be true. A close reading of the rules permits a hitter to change batter’s boxes between pitches, as long as there aren’t two strikes on him. Of course, who has ever seen a hitter do this? One could conjure a scenario where this might give the hitter some kind of edge, but in practice nobody cares to try it.

But why does this platoon exist? With handedness, the angles at which various pitches approach the plate can give one kind of batter a better chance at hitting them well. With batted-ball trajectory, I postulate that we see the effects of tendencies either adding together or cancelling out.

With two flyballers facing each other, the high angles they’re both seeking could often add up to pop-ups, easy plays for fielders. With two groundballers, added downward trajectories could turn a sharp two-hopper through the infield into a little dubber the pitcher easily scoops up. And when one type faces another, they may strike a balance.

Between grounders and flies sits the zone of the line drive, well and away the most productive of the three main classifications of batted balls. If one players wants a fly and the other a grounder, a stalemate between their tendencies might produce a bounty of liners. This could go a long way to explaining why the opposite trajectory platoon is better for hitters than a same-type platoon.

It is this last possibility that I looked into: whether matches between strong opposite platoons produce more liners, and thus more offense, than strong like platoons. I happily picked up a few other facts along the way, but the trajectory platoon was my starting point.

For the 2013 and 2014 seasons, I gathered statistics for each hitter who had at least 150 plate appearances in each season, and for each pitcher who threw at least 50 innings. I made the pitchers’ threshold low so I would get a fair sample of relievers in with the starters; the batters’ threshold was kept low to match. This gave me 399 and 394 batters for ’13 and ’14, plus 326 and 330 pitchers.

In each year, I separated out the 10 percent of players with the highest ratio of ground balls to fly balls, and the 10 percent with the lowest ratio. I tallied up the batted ball types (grounder, liner, fly) in all plate appearances involving members of those groups. (I excluded bunts because they seek a very specific type of hit, and because there is no such thing as a line drive bunt.) As control groups, I also took the middle 10 percent of hitters and pitchers to compare to each other.

As my first sidebar, I did find that strong trajectory tendencies for batters do persist year to year. Among the 40 batters in the top decile of grounders in 2013, 19 of them were in the top decile in 2014, with five others not playing in the majors at all that season. For top-decile flyballers, 16 of the 40 maintained their place in 2014, with three others out of the majors. Neutral tendencies don’t persist: the number for the middle 10 percent was just three out of 40.

Pitchers showed a lower rate of persistence at the extremes. For ground ballers, 11 out of 33 stayed in the top decile from ’13 to ’14, while nine out of 33 extreme fly ballers carried over. Compared to an eight of 33 rate for the middle cohort, persistence for pitching outliers is slight. (I was also able to check groundball pitchers from 2012 to 2013, where 13 of 33 stayed in the top decile. This higher rate, along with the small samples overall, makes me less inclined to suggest that there is no persistence for pitchers.)

Back on the original topic, the trajectory data do support my theory. The tables below show rates for all four platoons, the meetings of the neutrals, and the league-wide numbers. Rounding keeps percentages from adding up evenly in a few cases. Total balls in play are given to show sample sizes; those for the majors are an approximation.

2014 Batted Ball Trajectories

Batter/Pitcher	GB%	LD%	FB%	Balls in Play
All/All	44.8	20.8	34.4	~125K
GB/GB	74.1	16.3	9.7	652
GB/FB	45.2	21.2	33.6	684
FB/GB	45.8	23.9	30.2	589
FB/FB	20.5	17.8	61.6	730
Neut./Neut.	43.4	21.4	35.1	1,068

2013 Batted Ball Trajectories

Batter/Pitcher	GB%	LD%	FB%	Balls in Play
All/All	44.5	21.2	34.3	~126K
GB/GB	69.0	17.8	13.2	870
GB/FB	40.9	22.4	36.7	687
FB/GB	46.7	22.2	31.1	807
FB/FB	23.9	18.8	57.3	756
Neut./Neut.	41.6	21.0	37.4	1,100

Both years, opposite platoons do better in line-drive percentage than matching platoons, average versus average, or the majors as a whole. The average/average match-ups were near enough to the league-wide numbers that I really could have gone with the latter, though it’s a good check to see the figures line up as closely as they do.

There’s no clear superiority to whether the batter in the good platoon is a ground ball or fly ball hitter, though the total numbers lean toward fly ballers hitting against ground ballers. Line-drive numbers in the bad platoons also sit a little higher for flyball hitters, adding some weight to the argument that they are better at producing liners.

But then I checked the total 2014 numbers for the grounder and fly cohorts, and found the opposite. The groundball batters had an average liner rate of 20.5 percent against the whole league, versus 19.6 percent for the fly ballers. I cannot quite call that conclusive, but it certainly keeps me from claiming any line-drive superiority for the extreme flyball hitters.

Another side angle that presented itself is which player has more effect over the trajectory of batted balls. The major league groundball/flyball ratio was 1.30 in both 2013 and 2014. I looked at the ratios for the various breakdowns, though for this table I left out the same-style platoons.

Grounder/Fly Ratios

Batter/Pitcher	GB/FB
All/All	1.30
GB/FB	1.22
FB/GB	1.51
Neut./Neut.	1.17

When facing his opposite style, the pitcher produces his kind of batted ball at rates better than the league average. His weight is greater in the scales. I won’t venture to put percentage values on pitchers’ and hitters’ contributions, especially due to the numbers put up by the neutral players against each other: more fly ball oriented than either platoon.

This inches into a point covered by The Book. Neutral pitchers fare more poorly against batters than pitchers on the extremes, grounder or fly. A lower grounder/fly ratio might explain some of this, as flies are more offensively productive than grounders (though the tables show no real change on those super-productive liners). It also suggests that having a plan to force one type of contact, ground or air, is better for a pitcher than just humming it up there and letting the batter dictate batted-ball type.

An opposite effect, though, seems to arise for batters. My data included plate appearances for the hitters, and I found an interesting pattern in how many they received. (Recall that this is based on a 150 PA minimum.)

Mean Plate Appearances for Batted Ball Types

Year	GB	Neut.	FB
2014	401.1	447.8	382.6
2013	387.9	424.5	407.3

Batters with neutral splits got more playing time than those on the extremes, by an average of 35 to 40 PAs. Also, players with fewer than 200 PAs numbered at least six out of both ground baller and fly baller cohorts in each year, but for neutral players numbered two and three for ’14 and ’13. This implies that the neutrals are better batters, whose managers get them out there more often. Whereas pitchers ought to be looking for one type of contact, batters apparently should not be—unless it’s liners.

This actually conforms to the traditional roles the two players have. Pitchers act; batters react. It therefore makes sense for the pitcher not to cede control of even one aspect of the encounter, and for the batter not to be too fully committed to a goal that the pitcher can guard against.

Regrettably, the nuggets I’ve unearthed aren’t as widely applicable as one might wish. The groundball and flyball categories, by design, cover just 10 percent apiece of batters and pitchers in the league. (In The Book, they go between 12 and 17 percent with their extreme trajectory buckets.) You can expect, on average, one extreme grounder hitter and one extreme fly hitter in a lineup, if that.

Despite that narrowness, we do see some solid conclusions. One of them is even the one I was hoping for: opposite trajectory platoons produce an elevated line-drive rate that helps batters perform better than against same trajectory pitchers. I do like seeing one of my hypotheses pan out. It happens seldom enough.

There is only so much, though, that a top-down analysis such as mine can reveal by drilling into the macro statistics. A bottom-up approach, looking at exact trajectories drawn from the PITCHf/x and HITf/x databases, could find far more. Hardball Times readers may find that here in the future. Perhaps from me; perhaps from somebody else.

References and Resources

• Acknowledgments to Tom Tango, Mitchel Lichtman, and Andrew Dolphin for The Book, the foundation of my work today (and many others’ on many occasions).
• Trajectory rates and specific batted-ball data came from FanGraphs, with Baseball-Reference providing additional figures.
• For any follow-up researchers: B-R uses different trajectory criteria, producing different line-drive rates than FG’s. Its grounder/fly ratio numbers are also greatly different, apparently because it counts line drives as flies.