The mysteries of the heater, the high hard one, baseball’s overpowering pitch, are explained by the game’s power pitchers, a physicist, a brain cognition expert and the hapless hitters who have to swing at smoke in “Fastball,” a very engaging documentary narrated by Kevin Costner.

Sports documentary director Jonathan Hock had access to them all — well, save for Randy Johnson and Steve Carlton — and manages a quite thorough dissection of the physics of speed, the illusion of the “rising fastball” and the burning question, “Who was the fastest?”

The quick answer might appear to be current Reds hardballer Aroldis Chapman, who one day hist 105 miles per hour on the radar gun in the middle of the game. But David Price and Craig Kimbrel and Justin Verlander are here and are in the conversation. Batters who have faced these guys (Derek Jeter) help make their case.

But baseball is a game of history and a font of myth. So Hock goes at the Big Question historically and methodically. And he gets experts, from sports writers and historians to the men who played the game, to parse the facts as we know them.

Walter Johnson, the “Big Train,” was the first fastballer of note. In the early years of the game, his pitches were the first described as “humming” as they zipped past you at the plate, the first that seemed almost unhittably hard. How hard? The U.S. Army and Remington firearms had this elaborate test range set up to time his pitches in the days before the movies had sound.

Bob Feller, “The Heater from Van Meter,” was equally dominant, and his 1930s and 40s pitches were tested against the fastest motorcycle of the day and other, more scientific means.

Koufax and Drysdale, and the great Bob Gibson (interviewed, and hilarious) are remembered for their intimidating speed. Batters who faced them (Hank Aaron, Johnny Bench, Joe Morgan and Mike Schmidt among them) joke about what it was like, facing them.

Every great hitter interviewed talks about the hardest hurler he ever faced. Wade Boggs? “Juan Berenguer (“Senor Smoke”) of the Twins.

“Myth” enters the picture with the story of the fellow who inspired “Nuke Laloosh” of the Ron Shelton movie, “Bull Durham.” Steve Dalkowski was in the Orioles farm system in the 1960s, was never accurately clocked, and was so wild he never made a mark in the big leagues. But his legend grew and grew. Insanely fast. Breaking boards in the backstop fast. Maybe the fastest ever, though the best case can certainly be made for Texan Nolan Ryan, the most dominant pitcher of all time.

SP.0611.Ryan13 — LOS ANGELES TIMES FILE PHOTO — Angels pitcher Nolan Ryan pitching against the Boston Red Sox at Anaheim Stadium on June 14, 1974. Ryan pitched 13 innings, struck out 19 and threw 235 pitches.

Most fascinating for me was the attempt to compare, using the science and standards of today and measurements (and film footage) from the earliest days of the sport. Johnson and Feller can be compared to Verlander and Chapman.

It’s a fun film, not quite as lighthearted as the similar “Knuckleball” documentary of a short while back, but amusing enough. And as another baseball season is about to begin, it makes a great warmup for another season and a greater appreciation for what the Boys of Summer face every time they step into the box against the high, hard one.

MPAA Rating:  unrated

Cast: Nolan Ryan, Hank Aaron, Aroldis Chapman, Bob Gibson, Derek Jeter, Rich Gossage, Wade Boggs, Johnny Bench, Justin Verlander, David Price, Torii Hunter, Mike Schmidt, narrated by Kevin Costner.
Credits: Directed by Jonathan Hock. A Gravitas Ventures release.

Running time: 1:25