on one's home ground
Where one has the advantage of familiarity. For example, Teams generally find it easier to win on their home ground, or The candidate from Maine was speaking on his home ground.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.