In 2009, Boxx signed to the Los Angeles Sol for the inaugural season of Women's Professional Soccer and was named team captain.
She started in 18 of the 19 matches she played for the Sol, scoring three goals with three assists.
Boxx was named to the WPS First Team and played in the WPS All-Star Game.
The Sol finished in first place during the regular season with a 12–3–5 record.

In 2010, she was signed to the Saint Louis Athletica during the Los Angeles Sol dispersal draft.

Later in the season after Saint Louis Athletica folded, she was traded to the FC Gold Pride.
Boxx helped the team win the WPS regular season title and championship.
 She started in 19 of the 20 games she played in, while scoring one goal and providing five assists.
She was a WPS All-Star Game starter and received the fifth overall votes.

For the 2011 WPS season, Boxx signed with magicJack and played 833 minutes in 10 games starting in them all.
 She helped the club make a run to the playoffs in the second half of the season and win the quarterfinal match against the Boston Breakers.
In 2009, Boxx signed to the Los Angeles Sol for the inaugural season of Women's Professional Soccer and was named team captain. She started in 18 of the 19 matches she played for the Sol, scoring three goals with three assists. Boxx was named to the WPS First Team and played in the WPS All-Star Game. The Sol finished in first place during the regular season with a 12–3–5 record.
In 2010, she was signed to the Saint Louis Athletica during the Los Angeles Sol dispersal draft.
Later in the season after Saint Louis Athletica folded, she was traded to the FC Gold Pride. Boxx helped the team win the WPS regular season title and championship.  She started in 19 of the 20 games she played in, while scoring one goal and providing five assists. She was a WPS All-Star Game starter and received the fifth overall votes.
For the 2011 WPS season, Boxx signed with magicJack and played 833 minutes in 10 games starting in them all.  She helped the club make a run to the playoffs in the second half of the season and win the quarterfinal match against the Boston Breakers.
Shannon Boxx