Three hundred and thirty feet from home plate, the right field fence at Comerica Park intersects the foul line at nearly a right angle. As we move away from the corner, the fence line remains perpendicular to the foul line well into right-center. But the simplicity of the geometry is interrupted by a perturbation that may have sprung from the imagination of a right-handed flyball pitcher. At a point 365 feet from home plate the fence juts away from the batter while simultaneously growing taller. This peculiar configuration leads to an enlarged expanse in deep right-center that corresponds to what analysts call the 89 zone. This region is sufficiently unique that over the last three years Comerica Park has yielded both fewer home runs and more triples to the 89 zone than any major league ballpark. Last year, for example, the only visiting players to reach the 89-zone seats at CoPa were Cargo and Trout who victimized Marte and Turner respectively. Despite the inviting dimensions in right before the fence juts and grows, the quirky geometry in right-center gives Comerica a left-handed batter home run park factor of 98 (100 is neutral) which means that pitchers are favored when a left-handed batter is at the plate. For those curious about zones, the 89 zone is the third angular slice as we move counterclockwise from the right field line in this diagram from retrosheet.org.
Eventually, we'll show how the Tigers use Comerica to their advantage. But as a first stop along the way, let's look at another ballpark. In contrast to Comerica, Miller Park is characterized by a longer distance of 345 feet down the right field line but is much easier to conquer in right-center as seen in this overlay from hittrackeronline.
Only Yankee Stadium and Coors Field have seen more home runs hit to the 89 zone than Miller Park over the last three years and, when you add it all up, Milwaukee's yard has a very favorable home run park factor of 106 for left-handed hitters.
As you might expect from the preceding discussion, Prince Fielder lost a few home runs with his move to Detroit. But a curious thing happened along the way. The 9 zone represents the two angular slices that are closest to the right field line in the zone diagram. During his seven years with the Brewers, Prince pulled 22.2 percent of his balls in the air to the 9 zone and hit 14.4 percent of his balls in the air to the 89 zone. For the purposes of this discussion, balls in the air refer to all line drives or flyballs that reach the outfield.
After his move to Detroit, the Prince pulled a higher fraction, 23.4%, to the 9 and hit a lower fraction, 9.1%, to the 89 in right-center. Things get even freakier when we isolate on Fielder's 2012 results at Comerica. Here the numbers say that, by luck or design, Prince's directional distribution of balls in the air was tuned to Comerica's geometry even more than his overall 2012 numbers. Fielder pulled 28.8% of his Comerica balls in the air to right where home runs come easy and hit just 6.4% to right-center where flyballs go to die. If you look at Fielder's year-by-year results at home, he matched his career high in 2012 with 36 air balls to the 9 zone and set his career low with just 8 balls to the 89. I can't help but wonder if Mr. Fielder adjusted his swing for CoPa or if this was all just a happy coincidence.
Either way, we're now ready to look at the big picture. At 50-31 last year, the American League champs finished one game behind the Yankees for the best home record in major league baseball. But the Tigers were a putrid 38-43 on the road. Why? Is it about sleeping in your own bed? Home cooking? The encouragement of the Comerica faithful? These things might help, but a significant part of the home/road disparity can be explained by the Comerica Park geometry.
Since the fences were moved in, Detroit's ballpark has been kind to right-handed batters. The most recent Comerica home run park factor for righties is a hitter-friendly 104 as compared to the aforementioned pitcher-friendly 98 for left-handed batters. The Comerica home team can exploit this asymmetry by using more right-handed batters than their opponent. On offense, the Tigers are well configured to make this happen. In 2012, Detroit sent up 56.9% right-handed batters which exceeded the AL average of 54.2%.
The Tiger pitching staff is even more effectively configured to take advantage of Comerica's outfield dimensions. Detroit pitchers are predominantly right-handed which means that opposing managers are enticed to attack with left-handed batters. Last year, to be specific, Tiger pitchers faced 50.6% left-handed batters which was the second highest fraction in the game to Cleveland's 50.9%. While these lefties enjoy the platoon advantage against Tiger right-handed pitchers, the Comerica dimensions tend to keep their flyballs in the yard. And balls that stay in the yard tend to get run down by Austin Jackson. In summary, Comerica favors right-handed batters and Detroit's hitting and pitching personnel have been assembled, perhaps intentionally, to ensure that the Tigers usually send up more right-handed batters than the other team.
Now let's hit some details. Sixty-four percent of the home runs hit by the Tigers and their opponents last year were near the lines in the 7 and 9 zones. This number jumps to 74% if we consider only the games in Detroit due to the difficulty of homering in Comerica to the bigger parts of the park. The ML average, in case you were wondering, is that only 57% of HRs are hit to the 7 and 9 zones. Overall, the Tigers and their opponents each hit exactly 100 home runs near the lines and these HRs were distributed to give the Tigers a small home field advantage. In Detroit, the Tigers outhomered their opponents 61-56 along the lines due in large part to Fielder's pull numbers referenced above. The Prince, in fact, finished second to Granderson in all of MLB in 9-zone HRs at home. If you've done the arithmetic, you know that the Tigers were outhomered slightly, 44-39, along the left and right-field lines on the road.
Things get more interesting when we consider the minority of home runs that get hit to the larger areas of the baseball field known as the 78, 8, and 89 zones. In these regions, the Tigers outhomered the opposition by an impressive 31-11 margin at home while getting outhomered 40-31 on the road. The details will follow, but a big part of the story is the left/right asymmetry discussed earlier in combination with a certain Tiger's unique ability to leave any part of any yard.
We've already discussed the 89 zone in right-center. Opponent left-handed batters hit 31 more balls in the air to this zone (135 to 104) than Tiger lefties which is consistent with the 420 extra PAs that opponent lefties received. But these balls could do little damage in Comerica. Likely due to small sample luck, Detroit actually outhomered the opposition 5-2 in the 89 zone at home. But on the road it was a very different story. Away from Comerica the opposition's right-center HR total jumped from 2 to 20 and the Tiger total jumped by only half as much from 5 to 14.
The Tigers had the advantage in the 78 zone in left-center. Last year Tiger right-handed batters hit 47 more balls in the air to this zone (183 to 136) than their opponents. As we've pointed out, Comerica does not contain these balls as well as their mirrors in right-center and, as a result, the Tigers enjoyed an overall 17-9 HR advantage in the left-center zone at home. In what might seem like somewhat of an anomaly, Detroit was outhomered 14-11 in the 78 on the road despite hitting more balls than their opponent in that direction. To a large extent, this was due to Miggy hitting only 2 of his 9 left-center HRs away from CoPa.
But Cabrera wins our hearts with his drives to dead center. Tiger pitchers did not allow a single home run to the 8 zone at home in 2012 which isn't too surprising given the 420 feet between home plate and the centerfield wall. But the Tigers hit 9 HRs to the centerfield zone in Comerica with five of those coming off the bat of the MVP. You might remember that two of those blasts occurred on the same day, June 2nd, against the Yankees. On the road, Tiger opponents had an easier time and tied the Tigers 6-6 on home runs to center.
Now let's zoom back out to view the big picture. The Tigers were 72 runs better relative to their opponents at home (+64) than on the road (-8) in 2012. And they were 29 home runs better relative to their opponents at home (+20) than on the road (-9) just on the minority of home runs hit between left-center and right-center. If we multiply 29 by the average value of a home run then we can explain almost two-thirds of the home field advantage just based on balls in the air to the middle of the diamond. So if somebody asks you about Detroit's home field advantage, you've got a big piece of the answer. If you're in a hurry, though, just tell them that there's more to it than Kate Upton.