PORT ST. LUCIE, Fla. -- When Kodai Senga grips his signature “ghost fork” pitch, he spreads his hand wide, placing his index finger on the outside edge of one seam, his thumb on another and his middle finger across the heart of the “horseshoe.” Ball in glove, Senga applies a bit of pressure to firm up his grip, before uncorking the ball toward home plate.

At its best, the result looks like it did at the end of Senga’s live batting practice session Sunday at Clover Park, where he enticed Pete Alonso to swing and miss at a ghost fork tumbling below his bat. That’s how the pitch earned both its name and reputation: like a ghost, you see it, then you don’t.

“It’s got a really cool nickname for a good reason,” Alonso said. “It makes a lot of guys swing and miss.”

The exact origins of the ghost fork moniker are unknown to Senga, who says he first heard the term floating around Japan about a decade ago. Exhibiting the pitch to an international audience at the 2017 World Baseball Classic, Senga haunted opposing batters with 16 strikeouts over 11 innings. But the ethereal nickname did not pique the curiosity of most Americans until Senga signed with the Mets this winter on a five-year, $75 million contract. The scouting report on him included an explosive fastball, some breaking ball variations -- and the ghost.

Although folks back home tend to call the latter pitch a forkball, Senga clarified that technically speaking, it’s probably a splitter. (He doesn’t use the term “ghost fork” himself.) Senga does not jam it as deep into his fingers as true forkball practitioners do; due to the injury risk, few have attempted that stunt since the days of Dave Stewart and Gaylord Perry. In fact, Senga’s grip is almost identical to the splitter grip of teammate Carlos Carrasco, who calls his variation a split-changeup. But Senga stuffs the ghost deep enough into his right hand that, when combined with an appropriate release point, it tumbles with a flight path unfamiliar to Major League hitters.

“The shape’s pretty good,” said reigning batting champion Jeff McNeil, who was among those to take live BP off Senga on Sunday. “It’s something I haven’t seen before.”

Mets pitching coach Jeremy Hefner explained that the uniqueness stems mostly from Senga’s release point, which creates a distinct angle and fading action. Because Senga is unaccustomed to both the larger American baseball and the steeper slopes of stateside mounds, he’s had trouble finding consistency with his ghost fork in the early days of Spring Training. After spiking several of them in the dirt during a bullpen session last week, Senga called the results “so-so.” Not counting the whiff of Alonso on Sunday, Senga admitted his signature pitch “needs to be worked on.” (Less so his fastball, which hit 98 mph, according to McNeil.)

Nonetheless, Senga’s new Mets teammates are intrigued by the novelty of it all. Francisco Lindor quipped that during the live BP session, he saw all of Senga’s pitches except the splitter, because “it’s the ghost ball.” McNeil and Alonso had their fun, too. Told afterward that Alonso never caught a glimpse of the splitter that struck him out, Senga broke into a wide grin.

“This is ghost,” he replied in English.