Baseball player Moe Berg, shown in Switzerland, is the subject of the documentary “The Spy Behind Home Plate.” (Handout photo from mTuckman Media/Courtesy of Linda McCarthy)

The promising documentary “The Spy Behind Home Plate” has a subject that should guarantee a home run: professional baseball player Morris “Moe” Berg, who played 15 seasons as shortstop and catcher, including two with the Washington Senators, before going to work for the U.S. government as an intelligence agent during World War II. The film has more than enough true material to fuel an effective thriller, but director Aviva Kempner doesn’t quite manage to bring this fascinating figure to life.

The son of Jewish immigrants from the Ukraine, Berg was born in Harlem in 1902. Berg’s skill on the diamond was his ticket to enter worlds not usually open to Jews at the time: Princeton University, where he played baseball, and, later, the big leagues.

Although Berg would pass the New York State bar exam, he defied his father’s wishes that he become a lawyer, pursuing baseball instead. His professional career began in 1923 as a shortstop with the Brooklyn Robins (a precursor of the Dodgers).

Sport was not Berg’s only interest. In the offseason, he used his earnings to travel and was far from a passive

Moe Berg played professional baseball for 15 seasons and also worked as a spy. (Handout photo from mTuckman Media/Courtesy of Irwin Berg)

tourist. In Paris, he studied Sanskrit at the Sorbonne. During the 1932 season, when Berg was a catcher in Washington, D.C., his linguistic proficiency got him invited to embassy parties that earned him a reputation as a womanizer.

In 1934, the U.S. fielded an all-star team, which included Lou Gehrig and Babe Ruth, to send to Japan. Berg, who had already visited the country and could speak the language, was a natural choice. Taking place at a time when tensions were flaring between the two nations, the series of exhibition games served as an unofficial diplomatic mission. For Berg, who brought along a 16mm movie camera — and a letter from the State Department giving him the OK to photograph the city — it was also a surveillance opportunity.

The Japan trip marks Berg’s emergence as an agent, which became official when he joined the Office of Strategic Services in 1943. But footage from the trip also helps reveal why Berg doesn’t light up the screen.

Images of the legendary Ruth from the 1934 tour reveal an irrepressible personality. His mischievous grin, the way he wiggles a little when he runs to base — the Sultan of Swat, as Ruth was known, had an unmistakable magnetism. Berg, on the other hand, who’s seen throughout the film in stills and silent films, was a more stoic player. He blended in, in other words. While this may have served him well in espionage, it’s not great on screen.

In “The Spy Behind Home Plate,” Berg comes across as intriguing, but less than charismatic.

Casey Stengel is said to have once joked that Berg could speak multiple languages — the exact number is unclear — but that he couldn’t hit in any of them. That crack may offer a clue as to why such a colorful character would make for a fairly dry film subject. In the end, “The Spy” doesn’t quite strike out, but it doesn’t make it past first base either.

Moe Berg, right, in a military jeep driven by his brother Sam in California during World War II (July 1942). (Handout photo from mTuckman Media/Courtesy of Irwin Berg)

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Two and a half stars. Unrated. Contains disturbing footage of nuclear bomb victims. 98 minutes.

Ratings Guide: Four stars masterpiece, three stars very good, two stars OK, one star poor, no stars waste of time.