Both Fall Classic teams agree: The series' special baseballs feel a whole lot different than those from the regular season.

HOUSTON – Pitchers and coaches from both the Dodgers and Astros complained Saturday night about the World Series baseballs—and this time the controversy is not just about liveliness. They say there is a new problem: the baseballs used in the World Series are slicker than the ones used in the regular season because of a difference in the grain of the leather. The slicker World Series balls particularly make it hard to throw a good slider, they claim.

“We had a well-pitched game tonight from both sides,” Astros pitching coach Brent Strom said after Los Angeles won Game 4, 6-2. “I’m not taking anything away from the players. I just want to know why? Why in the world would the baseballs in the World Series be different? Because you can see the difference. You can feel it. I don’t understand it at all.”

Said Dodgers pitching coach Rick Honeycutt, referring to his Game 3 starter, Yu Darvish, “Yu noticed the difference. He told me the balls were slicker and he had trouble throwing the slider because of how slick they were. He wasn’t able to throw his slider the same way.”

Peter Woodfork, senior vice president, baseball operations, of Major League Baseball, said World Series balls are tested at the time of manufacturing and are made from the same materials and to the same standards as regular season baseballs. “The only difference is the gold stamping on the baseballs,” he said, a switch from the blue ink used during the regular season.

Major league baseballs are manufactured in Costa Rica, using cowhide for the cover. An MLB source speculated that how the baseballs were treated with the pregame rubbing mud before Game 4 could have led to a perceived problem.

Strom showed SI two baseballs side by side: a baseball used in World Series Game 4 and a regular season baseball. The regular season ball had not been prepared for a game with the specialty mud that umpires or their attendants rub into baseballs to reduce the shine and slickness. Even accounting for that difference, the leather grain of the World Series ball looked and felt noticeably different. It was slicker to the touch.

Houston pitching coach Brent Strom holds a 2017 regular season baseball (left) and a 2017 World Series ball. Tom Verducci/SI

During the ALDS, I heard from Cleveland Indians staff members that the postseason ball felt different from the regular season ball. Like the World Series ball, the postseason ball used in the LDS and LCS is stamped with different ink and logos than the regular season baseball.

“It’s obvious,” Strom said about the World Series ball being slicker. “You can see it and you can feel it. It’s not the same. Someone’s got to explain to me why.”

“Lance McCullers took the blindfold test in the bullpen,” said Charlie Morton, Houston’s Game 4 starter, referring to another Astros pitcher. “He could tell which ball was which with his eyes closed. It’s that different.”

Said Houston pitcher Justin Verlander, “The World Series ball is slicker. No doubt. I’m telling you, we’re in here signing [World Series] balls before the game, and it’s hard to get the ink on the ball sometimes. You know when you sign a receipt at Starbucks, and if you don’t hold the paper down with your hand, the pen just slides across the paper and the ink doesn’t stick to it? That’s what it’s like sometimes trying to sign these balls. That’s how slick the leather is.

“It’s different. I noticed it especially throwing a slider. It didn’t feel the same. The home run I gave up to [Joc] Pederson was a slider.”

Verlander threw 17 sliders in Game 2 and obtained only one swing and miss on the pitch. It equaled the fewest swings and misses on his slider for any of his 36 starts this year of more than two innings.

Said Darvish, “I had trouble with the ball throwing a slider. It was slicker.”

Darvish lasted only 1 2/3 innings in Game 3, especially because his slider, his signature pitch, was so bad. Darvish threw 14 sliders and did not get a single swing and miss on the pitch. It was the first time in 34 starts this year that Darvish did not get a swing and miss on his slider.

Batters had hit just .109 against Darvish’s slider since he joined the Dodgers. It is considered one of the best sliders in the game. But the metrics on the pitch showed it was noticeably worse in Game 3 than it had been during the regular season, such as a horizontal break of 8.42 inches, down from 9.12 during the season.

In Game 4, Dodgers closer Kenley Jansen gave up a home run on a slider to Alex Bregman. It was the first time all year Jansen gave up a home run on a slider, covering 96 sliders.

No pitcher is having a worse time with his slider lately than Houston closer Ken Giles. During the regular season, Giles threw his slider 47 percent of the time and held hitters to a .133 batting average with it. But the pitch has been so unreliable in the postseason that Giles threw only two sliders among his eight pitches in Game 4 – both of them balls. Entering a 1-1 game to start the ninth inning, Giles faced three batters and retired none of them. He was charged with three runs and the loss.

During the regular season Giles threw his slider out of the strike zone 51 percent of the time. In the postseason he has missed with that pitch a whopping 74 percent of the time, including 75 percent in the World Series (9 of 12). Able to eliminate the slider, Dodgers hitters are sitting on his fastball and teeing off on it. They are hitting .800 against his fastball (4-for-5), with all of those hits coming on hitters’ counts or first pitches (2-1, 3-1, 1-0 and 0-0).

Game 4 actually was a 1-0 pitchers’ duel through six innings between Morton and Alex Wood. Neither pitcher throws a slider. The seven relievers that followed them combined to throw only 12 sliders–and obtained no swings and misses on those sliders. Though he doesn’t throw a slider, Morton said the slicker baseball did influence his pitch selection.

“It affects running my two-seamer in to righthanders,” said Morton, who hit 97 mph with his two-seam fastball. “When the ball is slick you can’t throw in with the same aggressiveness. If you don’t have control of the baseball, you might end somebody’s career. That’s a very bad thought to have in your head.

“Tonight, it’s the World Series. So you do everything you can to block out everything. You’ve got to focus with every pitch. But I don’t know, maybe it’s the placebo effect, but if that’s what you’re thinking about it does affect your conviction on certain pitches.”

Said Honeycutt, “I know guys have been talking about the ball. I also know that MLB has been talking for a while about maybe a ball that’s more like the ball in Japan, where the leather is tackier so that you can use it right out of the wrapper. I think something has to be done.”

After a record-setting regular season with the most home runs all time, 6,105, the rate of home runs has shot up 35 percent in the World Series, from one every 27.1 at-bats in the regular season to one every 17.5 at-bats in the World Series.

There have been 15 home runs hit in this World Series already. Only eight of the previous 112 World Series had more.