Nathan Winston Kirby (born November 23, 1993) is an American former professional baseball pitcher. He was drafted 40th overall by the Milwaukee Brewers in the 2015 MLB draft, but would never play in Major League Baseball (MLB).

Kirby attended James River High School in Chesterfield County, Virginia.^[1] As a senior, he was the Virginia Gatorade Baseball Player of the Year^[2] after going 9–1 with a 1.24 ERA and 90 strikeouts in 56+2⁄3 innings pitched.^[3] He declared himself ineligible for the 2012 Major League Baseball draft after electing not to fill out certain drug tests and medical forms that are required by Major League Baseball.^[4][5]

As a freshman at the University of Virginia in 2013, Kirby pitched in 24 games and made two starts. He finished the season 4–1 with a 6.06 earned run average (ERA) and 37 strikeouts in 32+2⁄3 innings. Kirby was one of Virginia starting pitchers as a sophomore in 2014. On April 5 he pitched a no-hitter with 18 strikeouts against Pittsburgh.^[6][7] He was named the co-Atlantic Coast Conference Pitcher of the Year and was named to the All-ACC First Team. He was also an All-American by Louisville Slugger and Baseball America.^[8][9][10] In 18 starts in 2014, he was 9–3 with a 2.06 ERA. As a junior in 2015 he compiled a 5–3 record and 2.53 ERA in 12 games (11 starts). He was named to the All-ACC First Team for the second year in a row. He ended the year by recording the final out on a called third strike as the Cavaliers defeated Vanderbilt in the College World Series final.

In 2023, Kirby returned to the University of Virginia to complete his degree.^[19]