Break new ground do something innovative and beneficial.
cut the ground from under someone's feet do something which leaves someone without a reason for their actions or opinions.
get something off the ground start or cause to start happening successfully.
go to ground (of a fox or other animal) enter its earth or burrow.
ground zero the ground under an exploding (nuclear) bomb; in the US, used to designate the site of the World Trade Center after it was destroyed by terrorist action, 11 September 2001.
See also have both feet on the ground, hit the ground running, shift one's ground.