John Alexander "Andy" Messersmith (born August 6, 1945) is an American former Major League Baseball right-handed pitcher. During a 12-year baseball career, he pitched for the California Angels (1968–72), Los Angeles Dodgers (1973–75 and 1979), Atlanta Braves (1976–77) and the New York Yankees (1978). As a member of the Dodgers, he appeared in the 1974 World Series.

Messersmith was born on August 6, 1945, in Toms River, New Jersey. His father John was a doctor. At the age of five his family moved to Orange County, California. He attended Woodrow Wilson High School in Long Beach, but transferred to Western High School in Anaheim from which he graduated.

In 1963, as a senior, the 6 ft tall (1.83 m) Messersmith had a 14–1 regular season won–loss record as a pitcher for Western's baseball team, a 0.75 earned run average (ERA), and a .344 batting average as a hitter. This was the only year he played primarily as a pitcher in high school. He ended the 1963 season 15–2 or 16–2 overall, losing in a close championship game. He had two no-hitters and a 17-strike out game. Western came in second the 1963 California Interscholastic Federation (CIF) AAA playoffs, and Messersmith was named first-team All-CIF as a pitcher and Sunset League Player of the Year. He was unanimously selected as the Orange County Player of the Year by the Orange County Sportswriters. He was also the school's quarterback in football, but did not play as a senior due to injury.

Messersmith originally wanted to attend the University of Southern California (USC), but the school only offered him half of a scholarship to play baseball. He received full scholarship offers from the University of California, Berkeley (Cal) and the University of California at Los Angeles (UCLA) and chose Cal. In 1965 as a Cal sophomore, he had an 8–2 record, while leading the California Intercollegiate Baseball Association (CIBA) with a 1.63 ERA. He was unanimously selected to the 1965 CIBA All-Star Team, and was named an All-American. He wanted a $50,000 signing bonus from any team that was asking him to leave college in 1965. The Detroit Tigers and/or Boston Red Sox drafted him in 1965, but he returned to play at Cal for another year. He had an 8–5 record in his junior year. Overall at Cal, he had a 16–7 record with a 2.00 ERA.

Following his junior year of college, the California Angels drafted Messersmith with the 12th overall pick in the June 1966 secondary amateur draft for players previously drafted but not signed within six months. That same month Roland Hemond, head of the Angels' farm system, signed Messersmith for approximately $65,000.

In 1966, the Angels assigned Messersmith to the Triple-A Seattle Angels of the Pacific Coast League (PCL). He started 12 of the 18 games in which he pitched, with a 4–6 record and 3.36 ERA. In 1967, he was sent down to the Double-A El Paso Sun Kings of the Texas League, where he started 18 games, with a 9–7 record and 4.34 ERA. In 1968, he played part of the season in Seattle again, starting 11 games with nine appearances as a relief pitcher, and going 6–7 with a 2.96 ERA.

Messersmith appeared in 28 games for the Angels in 1968, starting five. He had a 4–2 record, three saves and a 2.21 ERA. In his September 6, 1968 debut as a starting pitcher, against 1967 Cy Young Award winner Jim Lonborg, Messersmith pitched at two-hit shutout, winning the game 4–0 against the Boston Red Sox.

Messersmith pitched a full season with the Angels in 1969. He started 33 games, with a 16–11 record, a 2.52 ERA, and 211 strikeouts in 250 innings pitched, with 100 bases on balls. He did this on a team that was 71–91, fifth worst in the American League (AL). He led all major league pitchers in least hits per nine innings pitched (6.084), had the AL's fourth best ERA among starting pitchers, fifth best WAR (wins above replacement) for pitchers (5.3), and third best strikeouts per nine innings pitched (7.596). In 1970, he was 11–10 with a 3.01 ERA, and led the AL in hits per nine innings (6.658).