Trapp wore the armband for Crew SC for the first time on May 17, 2014, and received the nod permanently ahead of the 2017 season.

On December 13, 2012, it was announced that Trapp had signed with his hometown Major League Soccer club, Columbus Crew, as a Homegrown Player.

He became the fourth HGP signing in club history, following in the path of Aaron Horton, Matt Lampson, and Ben Speas.

[14] After missing the early part of his first season while on international duty, Trapp made his professional debut for the Crew on July 7, 2013, starting and playing the full ninety minutes in a 1–0 victory against Portland Timbers; he was named as the club's man of the match after completing 86 percent of his passes.

[15] Trapp started the final sixteen matches of the season for Columbus, earning a postseason nod as the club's Breakout Performer of the Year.

[4] Ahead of his second professional season, Trapp was named as the vice captain for Columbus, serving as understudy to Michael Parkhurst.

His first serious injury with Columbus was suffered in April, a concussion that saw him miss thirteen total matches stretching through the end of June.

He missed the entire month of September after suffering a concussion in late August, sitting out four matches before returning to the field.

[26] Columbus traded Parkhurst to Atlanta United ahead of the 2017 season; to take his place, Trapp was elevated to the role of captain.

[27] In his first season as captain, Trapp started all 40 games that Columbus played: 34 in the league, five in the playoffs, and one in the U.S. Open Cup.

[28] Trapp set multiple personal records on the season, tallying his career-high in assists with five, minutes played with more than 3,000, and earning three MLS Team of the Week nods.

[4] Although Trapp remained as captain for the 2018 season, the leadership council behind him was updated, consisting of Ricardo Clark, Higuaín, Hector Jiménez, Jonathan, Zack Steffen, and Williams.

His strike from nearly forty yards out, coming two minutes into second-half stoppage time, handed Crew SC all three points and was named as MLS Goal of the Week.

[36] As the camp did not include a match, Trapp had to wait until June 6 to make his official debut for the team, starting a 4–2 defeat against Uruguay at Estadio Gran Parque Central.

Trapp capped his time with the U20s at the World Cup, playing all 270 minutes and captaining the side against France, although the United States failed to progress out of the group stage.

[45] He would keep the armband for the next few matches for the United States, notably a 1–1 draw with eventual 2018 FIFA World Cup champions France on 9 June.