On May 19, Mariners third baseman Kyle Seager looped a rolling Jose Quintana slider off the end of his bat and into short right field. Seager didn't hit the ball hard, but the falling liner would have been a hit in any other era in baseball history, a soft single landing safely over the second baseman's head.
Of course, in the modern game, nothing is guaranteed for a left-handed batter who hits the ball on the ground. Though Seager lofted the ball slightly, it still landed in front of White Sox second baseman Yolmer Sanchez, who scrambled to corral the one-hopper and tossed out Seager by a step. With a 92 percent hit probability, it went in the box score as a 4-3 putout, but was tied for the least likely groundout of last season. Seager busted it down the line, smelling a hit he knew he should have had.
The shift isn't new, and it isn't going anywhere. We know that it works, at least more often than not, because teams would stop using it otherwise. But determining how well it worked, exactly, used to seem undecipherable.
Now with Statcast™, we can use several different data points to tackle questions previously reserved for intrepid front-office staffs. How well does the shift work on individual hitters? Whose numbers does it affect the most? Who is the best at beating it?
Let's take a Statcast™ dive into the frustrating world of hitting against the shift, where helmets get slammed, tensions run high and beating the ball into the ground ultimately affects your bottom line.
Who gets shifted on the most?
The obvious answer to this question is "powerful left-handed hitters," though shifts against righties (and less dangerous lefties) have increased in recent years, as well. The six hitters who faced the most shifts last season were left-handed, followed by three switch-hitters and then seven more full-time lefties. Anthony Rizzo saw the most, with 370. Seager faced the next most, followed by Mike Moustakas, Jay Bruce, Mitch Moreland, Rougned Odor and three switch-hitters: Carlos Santana, Kendrys Morales and Justin Smoak.
Who was hurt most by the shift?
For this exercise, we'll use the Statcast™ metric called expected batting average (xBA), which predicts what a hitter should have hit based on the quality of contact, combining exit velocity and launch angle. If we narrow xBA to focus only on a hitter's ground balls, then find the difference between that and his actual batting average on grounders, we begin to get a picture of how much an abnormal defensive alignment could've cut into those numbers.
Brandon Belt, Giants -- shifts faced: 220
xBA on grounders: .328
BA on grounders: .163
Difference: -.165
Belt has a case for the hitter hurt most by the shift in 2017. Thirty hitters faced more shifts than Belt, but none lost more xBA on pulled grounders, mainly because Belt pulled 61 percent of his grounders (fifth most among qualified lefties). Belt lost 165 points of batting average on grounders, and a whopping 321 points when exceeding Statcast™'s hard-hit threshold of 95-mph exit velocity. Those would-be hits would've made a sizeable difference in Belt's .241/.355/.469 slash line.

Smoak, Blue Jays -- shifts faced: 303
xBA on grounders: .277
BA on grounders: .115
Difference: -.162
Switch-hitter Smoak's 303 shifts faced ranked ninth most in the Majors, and made a dent in the first baseman's production, which was still impressive. The shift squeezed 162 points of batting average out of Smoak's grounders, and 334 points when he hit those grounders hard.
Joey Gallo, Rangers -- shifts faced: 195
xBA on grounders: .289
BA on grounders: .162
Difference: -.127
Gallo never tries to hit the ball on the ground, probably because he's nearly an automatic out when he does. Much of that stems from his propensity to pull -- no lefty pulled a higher percentage of his grounders last season (70.8 percent). So, even a relatively modest number of shifts employed against him (42nd most) resulted in a 127-point difference between Gallo's xBA and BA on grounders, the fifth-widest gap among qualified lefties.

Lucas Duda, Mets/Rays -- shifts faced: 240
xBA on grounders: .280
BA on grounders: .154
Difference: -.126
Defenses have long shifted against Duda, who can drive the ball well to the opposite field, but rarely grounds it that way. Duda should have hit .442 on hard-hit grounders, according to xBA, but his actual average on those grounders limped in at .194. That 248-point difference ranked third worst across baseball.
Who avoided the shift the best?
Rizzo, Cubs -- shifts faced: 370
xBA on grounders: .241
BA on grounders: .162
Difference: -.079
Ironically, some of the hitters who defied the shift were shifted on the most. Rizzo faced more shifts than anyone in baseball, but lost just 68 points of batting average on hard-hit grounders. Thirty-five hitters surrendered more.

Seager, Mariners -- shifts faced: 369
xBA on grounders: .286
BA on grounders: .250
Difference: -.036
The hit Seager was robbed of in May was actually one of relatively few he surrendered to the shift. Seager faced the second-most shifts in baseball, but lost just 36 points of batting average on grounders (32nd most), and 143 points on hard-hit grounders (12th most). It could have been much worse for him.
Matt Carpenter, Cardinals -- shifts faced: 276
xBA on grounders: .315
BA on grounders: .250
Difference: -.065
Carpenter has pulled the ball more over the last two seasons. Last season, he slid in behind Gallo with the second-highest pull percentage on ground balls (69 percent) among lefties. As a result, Carpenter ranked 12th in shifts faced. Still, when he hit the ball hard on the ground, he lost fewer points of batting average than 47 other hitters.
Bruce, Mets/Indians -- shifts faced: 338
xBA on grounders: .272
BA on grounders: .218
Difference: -.054
This slugger ranked in the top six in ground-ball pull rate and shifts faced, but just 20th in xBA lost on grounders (53 points) and 30th on xBA lost on hard grounders.

Who should be shifted on more?
Clubs do a great job of recognizing most hitters' weaknesses and capitalizing on them quickly. One hitter they're still trying to figure out, though, is Rockies center fielder Charlie Blackmon, who led the Majors in hits and runs in 2017.
Shifting on Blackmon more might tamp down those numbers. Blackmon pulls 47 percent of his grounders, which makes him one of baseball's 30 most pull-happy hitters. But he gets shifted on in just one of every seven plate appearances. All that exposed grass helped Blackmon to a .308 average on ground balls in 2017, seventh highest in baseball.
Shift data from FanGraphs