Does bunting make more sense in today's MLB?

Jerry Lai / USA Today

Sunday afternoon, the White Sox looked like they were about to be the latest victims of Rays ace David Price. Price allowed just two hits through the first five innings, struck out five, and finished four of the first five innings in 1-2-3 fashion. 

Down 1-0 in the sixth, Chicago mustered a pair of baserunners thanks to a Ben Zobrist error and an infield single. Next up for the White Sox was Marcus Semien, a .240/.279/.385 career hitter who had already popped out and struck out against Price. White Sox manager Robin Ventura called for a bunt.

Semien's bunt was far from textbook, as he allowed the bathead to drop well below the hands and popped it up. But he managed to drop it in the no-man's land between the third baseman, pitcher, and catcher. Price pounced on the ball, but threw the ball into the outfield in his haste. 

After another error by right fielder Wil Myers getting the ball back into the infield, both runners scored and Semien wound up at third base. The White Sox scored five runs in the sixth inning and won in a 9-2 romp. The White Sox gained 22 percent in win probability on the play, the biggest swing of any in the game.

Source: FanGraphs

Thus far, 2014 has been the season of the bunt. Semien's big bunt was just one of three thus far to add at least 20 percent of win probability. 

Through Sunday's action, non-pitchers laid down 310 bunts this season, leading to 89 hits, 13 errors, 123 sacrifices, 82 outs and three double plays. According to the Baseball-Reference Play-Index, these 310 bunts have been worth a staggering plus-2.5 wins by Win Probability Added and plus-17 runs by RE24, a run-expectancy metric based on the runners on base and number of outs in the inning.

Over 600 plate appearances, the league's bunt performance comes out to plus-4.84 WPA (roughly equivalent to Josh Donaldson's 2013 performance) and plus-32.9 RE24 (roughly equal to Hunter Pence's 2013 performance). That is, bunting with position players has worked out really, really well this year.

What gives? 

One of the earliest sabermetric findings, dating back to Pete Palmer, is that the sacrifice bunt is a suboptimal play. This was only reinforced by later sabermetricans like Tom Tango and Mitchel Lichtman, and is a prevailing aspect of sabermetric thought for years.

While this is certainly still true in the general case — outs are valuable, and in general, a runner on first with no outs is preferable to a runner on second with one out — applying the general case across the board ignores how strategic decisions should change depending on game context. 

Bill James, initially a detractor of the bunt like most prominent sabermetricians, came to this realization as well. As he wrote in his Guide to Baseball Managers: 

"Time passes; there are other books and other prophets. The number of bunts per game has gradually increased since 1984, reaching as high as 80 per hundred games (1993). And I've had second thoughts, and I've done some additional research. I am no longer convinced that the sacrifice bunt is a poor percentage play."

James presents a number of reasons why the bunt, when deployed correctly, is a smart play. There are situations — generally, close and late as the home team — when playing for one run leads to a higher win probability than playing for the big inning. The run expectancy numbers that drive the conversation are based on the average hitter, and could change significantly based on the quality and tendencies of the hitter. As James put it:

"No one believes that having runners on first and second with one out is a better deal (for the defense) than having us a man on second with one out. But if Barry Bonds is at the plate and Rikkert Faneyte is on deck, you still might order the walk. The advantage you're going for doesn't reside in the inherent situation; it resides in the identity of the hitter. The same might well apply to the sacrifice bunt."

Managers, it appears, agree with James here. Observe, the 20 position players to attempt at least four bunts thus far in 2014:

Player Bunts ZiPS wOBA
Billy Hamilton 11 0.302
Leonys Martin 9 0.318
Danny Espinosa 8 0.287
David Lough 7 0.296
Dee Gordon 7 0.277
Eric Young 7 0.292
Starling Marte 6 0.326
Jonathan Villar 5 0.289
Brandon Barnes 5 0.300
Jarrod Dyson 5 0.276
Ben Revere 5 0.298
Bryce Harper 4 0.382
Scooter Gennett 4 0.306
Nori Aoki 4 0.312
Jean Segura 4 0.324
Christian Yelich 4 0.328
Will Venable 4 0.315
Junior Lake 4 0.297
Emilio Bonifacio 4 0.292
Alcides Escobar 4 0.280
TOTAL 111 0.303

Bryce Harper stands out as the only slugger on the list, but as a speedy left-hander, he is a prime candidate to catch a third baseman off balance with a bunt. 

Mostly, though, this list contains speedsters without pop, the kind of players that can bunt for a hit even when the defense expects it, and the kind of players that aren't likely to make much out of the plate appearance they're giving up. A weighted average of their projected wOBAs comes out to .303, or exactly what Dan Uggla and Andrelton Simmons posted in 2013. Opportunity cost is low, the chance of a hit is high, and a failed bunt will typically still result in a runner in scoring position.

The leaguewide improvements in pitchers and defenders have made it harder and harder on major league hitters. The league's .316 OBP would be the lowest mark since 1964. 

As such, the opportunity cost of a bunt is as low as it has been in 50 years. Hitters, particularly the hitters likely to get the bunt sign, are less likely to reach base in the first place than ever before. The advantage of these bunts, as James put it, resides in the identities of these hitters. Managers have done an excellent job thus far of picking spots, and the hitters have executed brilliantly. 

Does this mean the bunt has become a smart play? Perhaps, perhaps not. I would suggest looking for an all-encompassing heuristic is a fool's errand and that context matters more than anything. Or, as James concluded his essay:

"What I'm saying is that I simply do not know. The answer, dear class, is rolling in the grass. I don't think the right number is zero, and I doubt that it's near zero, but I don't know what it is. Having thought about the issue at great length, having worked hard to analyze the math involved, I can only tell you that there is no definitively correct mathematical answer at this time. Earl Weaver may have been right; Billy Southworth may have been right. Maybe each of them had the right answer for his own team. The rest of us need to keep an open mind."

Does bunting make more sense in today's MLB?
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