[1] In the summer of 1998, he played collegiate summer baseball in the Cape Cod Baseball League (CCBL) with the Wareham Gatemen, and returned to the CCBL in 1999 to play with the Orleans Cardinals, where he was a teammate of fellow future Major Leaguer Mark Teixeira.

In August, against the Idaho Falls Chukars, Sheets struck out eight batters while allowing just one hit through five innings.

In his seven minor league starts that year, Sheets averaged a strikeout ratio of 10.09 batters per nine innings.

[4] He pitched 22 innings, struck out 11 batters, walked one, and gave up 11 hits during the tournament, and faced off against Cuban ace Pedro Luis Lazo in the gold medal game, giving up three singles and advancing just one runner to second base for the entire game.

[4] Over the final two months of the season, Sheets pitched poorly and finished the year 11–13 with a 4.45 ERA.

[4] That season he also struck out 18 batters in a May 16, 2004, game against the Atlanta Braves, shattering the franchise record of 14, set by Moose Haas in 1978.

[6] By the end of the season, Sheets established himself as a strikeout threat, throwing 264, to finish second in the National League and third in the majors behind Randy Johnson and Johan Santana.

A series of inner ear infections that caused dizziness and a loss of balance forced Sheets onto the disabled list for a period of time in the beginning of the 2005 season.

In his second game back, he would pitch nearly a complete-game shutout, but in the 9th inning, Sheets gave up a two-run homer to Ken Griffey Jr. of the Reds.

In 2007, Sheets started both his and the Brewers' season on a high note by throwing an Opening Day complete game, two-hitter against the Los Angeles Dodgers.

[9] In his second start, Sheets threw only the second complete-game shutout of his career, beating the San Francisco Giants 7–0 in a five-hit, eight-strikeout performance.

In his 2008 All-Star outing, he pitched two scoreless innings, giving up one hit, walking two, and striking out three.

[14] At the end of the season, he incurred a tear in his right elbow, underwent Tommy John surgery and did not pitch in the postseason.

[17] Sheets got the Opening Day start, going five innings allowing three runs (two earned) on four hits while striking out three and walking four, receiving a no-decision.

On July 29, 2010, the Athletics announced Sheets would miss the remainder of the season due to a torn flexor in his right elbow.

[citation needed] On June 13, 2014, Sheets was inducted into the Brewers Wall of Honor for pitching over 1,000 innings with the club.