The most participants in a ground breaking ceremony is 6,256 achieved by the San Jose Earthquakes on the grounds of their new stadium in San Jose, California, USA, on 21 October 2012.
A member of Major League Soccer (USA), the Earthquakes provided 6,000 shovels for fans of the team, as well as allowing additional fans to bring their own, to break ground on the pitch of its new football (soccer)-specific stadium.
Please note: Comments below may relate to previous holders of this record.