For many reasons, I think the notion of these "ground games" is suspect, and the latest "ground game" casualty is Scott Walker, who supposedly had a massive "ground game" in one state and couldn't do squat. We'll see.
If you think that, you don't know how a well organized ground game turns into actual votes. Republican Voter names are taken from the last Republican Primary voter list, then contacted individually by people they know in their counties, Cruz paid workers organize all this from a Republican office they opened in every county, mail fliers come almost every day to Republican voters, then these voters are contacted when early voting starts, reminding them to vote and even taking them to the poll if they need transportation. This gets actual votes for the candidate and he more than likely wins, especially if the other candidates have no or little ground game. I've been part of such a ground game and I know it works.