Jeffrey Wayne Karstens (born September 24, 1982) is a former right-handed starting pitcher in Major League Baseball (MLB).

Karstens attended Mount Miguel High School in Spring Valley, California and initially played as a catcher.

He played the 2005 season with the Yankees' Double-A affiliate, the Trenton Thunder, posting a 12–11 record with a 4.15 ERA and 147 strikeouts.

In that outing, Karstens walked 2, struck out 1, and earned his first career Major League victory.

[5] In spring training prior to the 2007 season, Karstens pitched well enough to make a case for the rotation.

[17] Following the end of the season, Karstens pitched for Team USA in the 2007 Baseball World Cup.

[1] On July 26, 2008, Karstens was acquired by the Pirates with José Tábata, Ross Ohlendorf, and Daniel McCutchen from the New York Yankees for outfielder Xavier Nady and pitcher Dámaso Marte.

[22] In 2009, Karstens was fined an undisclosed amount by Major League Baseball for hitting Milwaukee's Ryan Braun squarely between his shoulder blades with a pitch in April.

[23][24] The Brewers took exception to this and later in the season Karstens was hit by a pitch in the left shoulder by a Milwaukee pitcher.

[29] Karstens was the pitching matchup in the highly anticipated debut of young phenom Stephen Strasburg.

Appearing in 30 games (26 starts), in which he went 9–9 with an ERA of 3.38, giving up 22 home runs, hitting 4 batsmen, walking 33, striking out 96, and having a WHIP of 1.207 through 162.1 innings.

[34] Karstens underwent surgery on his rotator cuff and labrum in his throwing shoulder on June 7, 2013, and was shut down for the rest of the 2013 season.