Hail Mary pass
A Hail Mary pass, also known as a shot play, is a very long forward pass in American football, typically made in desperation, with only a small chance of success. 

The expression goes back at least to the 1930s, when it was used publicly by two former members of Notre Dame's Four Horsemen, Elmer Layden and Jim Crowley. Originally meaning any sort of desperation play, a "Hail Mary" gradually came to denote a long, low-probability pass, typically of the "alley-oop" variety, attempted at the end of a half when a team is too far from the end zone to execute a more conventional play, implying that it would take divine intervention for the play to succeed. For more than 40 years, use of the term was largely confined to Notre Dame and other Catholic universities.

The term became widespread after a December 28, 1975, NFL playoff game between the Dallas Cowboys and the Minnesota Vikings, when Cowboys quarterback Roger Staubach said about his game-winning touchdown pass to wide receiver Drew Pearson, "I closed my eyes and said a Hail Mary."

Origins 
Crowley often told the story of an October 28, 1922, game between Notre Dame and Georgia Tech in which the Fighting Irish players said Hail Mary prayers together before scoring each of the touchdowns, before winning the game 13–3. According to Crowley, it was one of the team’s linemen, Noble Kizer (a Presbyterian), who suggested praying before the first touchdown, which occurred on a fourth and goal play at the Georgia Tech 6-yard line during the second quarter. Quarterback Harry Stuhldreher, another of the Horsemen, threw a quick pass over the middle to Paul Castner for the score. The ritual was repeated before a third and goal play, again at Georgia Tech’s 6-yard line, in the fourth quarter. This time Stuhldreher ran for a touchdown, which sealed the win for Notre Dame. After the game, Kizer exclaimed to Crowley, "Say, that Hail Mary is the best play we've got." Crowley related this story many times in public speeches beginning in the 1930s.

On November 2, 1935, with 32 seconds left in the so-called "Game of the Century" between Ohio State and Notre Dame, Irish halfback Bill Shakespeare found receiver Wayne Millner for a 19-yard, game-winning touchdown. Notre Dame head coach Elmer Layden, who had played in the 1922 Georgia Tech game, afterwards called it a "Hail Mary" play.

An early appearance of the term was in an Associated Press story about the upcoming 1941 Orange Bowl between the Mississippi State Bulldogs and the Georgetown Hoyas. The piece appeared in several newspapers including the December 31, 1940, Daytona Beach Morning Journal under the headline, "Orange Bowl: [Georgetown] Hoyas Put Faith in 'Hail Mary' Pass". As the article explained, "A 'hail Mary' pass, in the talk of the Washington eleven, is one that is thrown with a prayer because the odds against completion are big."

During an NBC broadcast in 1963, Staubach, then a Navy quarterback, described a pass play during his team's victory over Michigan that year as a "Hail Mary play". He scrambled to escape a pass rush, nearly getting sacked 20 yards behind the line of scrimmage before completing a desperation pass for a one-yard gain.

Examples 

Arguably the most memorable and replayed Hail Mary pass came on November 23, 1984, in a game now known as "Hail Flutie". Boston College was losing to Miami (FL) with six seconds left when their quarterback Doug Flutie threw a 52-yard touchdown pass to Gerard Phelan, succeeding primarily because Miami's secondary stood on the goal line to keep the receivers in front of them without covering a post route behind them. Miami's defense was based on the assumption that Flutie could not throw the ball as far as the end zone, but Flutie hit Phelan in stride against a flatfooted defense a yard deep in the end zone. To commemorate the play, a statue of Flutie in his Hail Mary passing pose was unveiled outside Alumni Stadium at Boston College on November 7, 2008.

Other noteworthy examples include:
 December 19, 1980: Known as "The Miracle Bowl", Brigham Young University quarterback Jim McMahon threw a 41-yard touchdown pass to tight end Clay Brown to defeat Southern Methodist University in the 1980 Holiday Bowl 46–45, which completed Brigham Young's comeback from a 45–25 deficit with four minutes remaining.
 September 24, 1994: Known as the "Miracle at Michigan", Colorado quarterback Kordell Stewart threw a 64-yard touchdown pass to wide receiver Michael Westbrook to beat Michigan 27–26 (Stewart's pass traveled 73 yards in the air from the Colorado 26 to the opposite 1 yard line, was tipped by Blake Anderson, then caught by Westbrook 4 yards deep in the end zone).
 October 31, 1999: The Cleveland Browns's first win after returning as an expansion team came on a Hail Mary against the New Orleans Saints, when Browns quarterback Tim Couch avoided the Saints pass rush and launched a 56 yard pass that was tipped up in the air and caught by receiver Kevin Johnson near the pylon for a 21–16 Browns victory.
 November 9, 2002: Known as the "Bluegrass Miracle", Louisiana State University quarterback Marcus Randall threw a 74-yard touchdown pass to wide receiver Devery Henderson in the game to defeat Kentucky 33–30.
 December 8, 2002: Three years after his first Hail Mary, Tim Couch won another game with a game-ender against the Jacksonville Jaguars. Couch launched a 50 yard Hail Mary that was caught by Quincy Morgan, and the ensuing extra point gave the Browns a 21–20 win. Although he remains a hotly debated player due to being picked #1 overall in the 1999 NFL Draft and his injury-plagued career, Tim Couch remains the only NFL player to win two games on game-ending Hail Marys.
 October 22, 2011: Known as "Rocket", Michigan State quarterback Kirk Cousins threw a 44-yard touchdown pass to wide receiver Keith Nichol to beat Wisconsin 37–31.
 November 16, 2013: Known as the "Prayer at Jordan–Hare", Auburn quarterback Nick Marshall threw a 73-yard touchdown pass to wide receiver Ricardo Louis on fourth-and-18 with 36 seconds left to beat Georgia 43–38.
 November 10, 2013: Sometimes a Hail Mary does not give a team a win. With the Baltimore Ravens leading 17–10 on the last play of their game against the Cincinnati Bengals, Bengals quarterback Andy Dalton launched a 51 yard Hail Mary to the end zone, where a Ravens player tipped the ball in the air directly to A.J. Green for a touchdown. Despite the wild game-tying score, the Ravens won the game in overtime, 20–17.
 September 5, 2015: Known as the "Miracle at Memorial", Brigham Young University quarterback Tanner Mangum threw a 42-yard desperation pass to wide receiver Mitch Mathews as time expired to defeat Nebraska 33–28. This play snapped a string of 29 consecutive home opener victories for the Cornhuskers. Mangum, a freshman just two months removed from a mission for The Church of Jesus Christ of Latter-day Saints, was the backup to senior Taysom Hill, who had left the game earlier with a season-ending Lisfranc injury. This game was Mangum's first organized football game in nearly four years.
 December 3, 2015: Known as the "Miracle in Motown", due to a defensive penalty on the Detroit Lions as the game clock ran out, the Green Bay Packers — who had been trailing the entire game — were given one additional play with no time left. Green Bay quarterback Aaron Rodgers threw a 61-yard touchdown pass, which was caught in the end zone by tight end Richard Rodgers to win the game 27–23. The ball left Aaron Rodgers' hand at Green Bay's 35-yard line and was caught a few yards into the end zone, making it the longest game-ending game-winning "Hail Mary pass" in the National Football League.
 January 16, 2016: In the postseason after the Miracle in Motown, Aaron Rodgers completed a second Hail Mary pass. Faced with 4th and 20 on his own 4-yard line and a 20–13 deficit against the Arizona Cardinals in the final minute of the game, Rodgers threw a 60-yard completion to Jeff Janis. Then, on the final play of regulation, he completed a 41-yard touchdown pass to Janis, making Green Bay the first postseason team ever to score a game-tying touchdown on the final play of the 4th quarter. However, Arizona won the game in overtime.
 September 10, 2016: After Oklahoma State football quarterback Mason Rudolph threw the ball up into the air as the clock ran out, it was ruled intentional grounding. Under college football rules, the game should have ended and Oklahoma State should have won the game. However, the officials (including Referee Tim O'Dey of the Mid-America Conference) gave Central Michigan an untimed down. Losing 24–27, Chippewas quarterback Cooper Rush threw a 49-yard Hail Mary to receiver Jesse Kroll who lateraled to Malik Fountain to run it into end zone winning the game 30–27.
 October 1, 2016: After a 47-yard touchdown pass with 10 seconds remaining on the clock, a Georgia player took off his helmet, resulting in a 15-yard celebration penalty. The kickoff was returned to the Georgia 43-yard line, and on the final play, Tennessee QB Joshua Dobbs threw a game-winning touchdown as time expired, to win 34–31.
 January 8, 2017: In a wildcard playoff game between the Green Bay Packers and the New York Giants, Aaron Rodgers completed a 42-yard pass to Randall Cobb over the heads of a crowd of players from both teams on the last play before halftime. This gave Green Bay a 14–6 halftime lead and they went on to win 38–13.
 September 16, 2017: In a key Southeastern Conference matchup between the Florida Gators and the Tennessee Volunteers, Florida quarterback Feleipe Franks completed a 63-yard pass to Tyrie Cleveland to earn the University of Florida a victory at the end of the game as time expired.

In other fields 
The term "Hail Mary" is sometimes used to refer to any last-ditch effort with little chance of success.

Military

In military uses, General Norman Schwarzkopf described his strategy during the Persian Gulf War to bypass the bulk of Iraqi forces in Kuwait by attacking in a wide left sweep through their rear as a "Hail Mary" plan.

There are similar usages in other fields, such as a "Hail Mary shot" in photography where the photographer holds the view finder of an SLR camera far from his eye (so unable to compose the picture), usually high above his head, and takes a shot. This is often used in crowded situations.

In computer security, a "Hail Mary attack" will throw every exploit it has against a system to see whether any of them work.