John Joseph Cust III (born January 7, 1979) is an American former professional baseball designated hitter and outfielder.

He played in Major League Baseball (MLB) for the Arizona Diamondbacks, Colorado Rockies, Baltimore Orioles, San Diego Padres, Oakland Athletics, and Seattle Mariners.

[4] In 1997, Cust, out of high school, was the first round draft pick (30th overall) of the Arizona Diamondbacks, and had a .447 on-base percentage in 35 games in the Rookie League.

In 11 minor league seasons with five different organizations, he hit exactly 200 home runs, had a .286 batting average, and a .429 on-base percentage.

On January 7, 2002, his 23rd birthday, he was traded by the Diamondbacks with catcher JD Closser to the Colorado Rockies for pitcher Mike Myers.

Cust spent the majority of the 2002 season with the Rockies' Triple-A affiliate, the Colorado Springs Sky Sox.

He was most noted as an Oriole for an infamous baserunning gaffe that resulted in his making the final out in a 12-inning 5–4 loss to the New York Yankees at Camden Yards on August 16, 2003.

During his 33 minor league game tenure, he hit .273 with 4 home runs and 19 RBIs, and matched his 33 Ks w/ 33 walks.

On September 13, Cust hit his 100th career home run in a 3–1 Athletics victory over the Kansas City Royals at Kauffman Stadium.

[17] In January 2012 Cust signed a one-year deal minor league contract worth $600,000 with an option for a second year with the Houston Astros,[18] but was released on March 27 before the end of spring training.

[21] On August 4, 2012, Cust was signed to a minor league contract by the Toronto Blue Jays and assigned to their Triple-A affiliate Las Vegas 51s.

After spending all of 2013 out of professional baseball, Cust resurfaced with the Orioles after signing a minor league deal on February 5, 2014.

[26] On December 13, 2007, Cust was named in the Mitchell Report as a user of performance-enhancing drugs, although there was never any evidence outside of a conversation he once supposedly had with former teammate Larry Bigbie.