He also played parts of five seasons with the Bridgeport Bluefish of the Atlantic League of Professional Baseball near his hometown.

Greenberg was also the team and area most valuable player in 1998, and helped lead Guilford to the state soccer title in 1996.

[1] There, he played college baseball for the North Carolina Tar Heels in the Atlantic Coast Conference (ACC).

[7][8] As a junior in 2002, he hit .337, stole 35 bases, scored 80 runs, homered 17 times, and again led the ACC with seven triples.

In 2003, when Executive Editor of Baseball America Jim Callis was asked whether he thought Greenberg had a chance to be a starter, or was destined to be a backup, he responded: "Very good character guy, often compared to John Cangelosi, more of a fourth or fifth outfielder.

'"[12] On July 7, 2005, Greenberg was called up to the Cubs' major league team from their West Tennessee Double-A affiliate.

[1][13] Greenberg suffered a concussion and a skull fracture as a result of the beaning and was immediately removed from the game and taken to a hospital.

As a result of the injury, Greenberg couldn’t sleep upright or even bend down to tie his shoes without losing his balance.

[12] He spent the rest of the 2005 season on the 15-day disabled list, and continued to suffer from positional vertigo, terrible headaches, nausea, double vision and dizziness.

Mike Downey of the Chicago Tribune, in an interview on June 6, 2006, compared him to Moonlight Graham, who 100 years earlier had appeared in his only Major League game, only to not get an official at-bat, a story recounted in the film Field of Dreams.

[16] Unable to gain a spot in the Triple-A Omaha Royals outfield, Greenberg was granted free agency by Kansas City.

[1] He faced De los Santos, who was pitching for the Long Island Ducks, the same pitcher who had hit him in the head in his sole Major League at-bat, and this time he singled.

In 2012, a Chicago Cubs fan started an online petition to get Greenberg another Major League plate appearance.

[19][20] The campaign succeeded when the Miami Marlins offered him a one-day contract to play in their October 2, 2012, home game against the New York Mets.

[26] The Aerosmith song "Dream On" was played through the stadium's public address system as Greenberg walked to home plate and the crowd gave him a standing ovation.

[23][26][27] He was struck out by Mets knuckleballer and eventual Cy Young Award winner[28][29] R. A. Dickey on three pitches and was removed from the lineup at the end of the inning.

"[31] He also said he wanted to continue his Major League career and hoped he would be invited to a team's spring training in 2013, ideally the Marlins.

Greenberg entered the first game of the tournament as a defensive replacement for left field, and walked during his sole plate appearance.