The Mets are 4-3 against the Giants this year, so I assume that if they finished in a tie for the first Wild Card spot, the do-or-die game would be played at Citi Field. The Mets are 3-3 against the Cardinals, so I'm not sure who would get home field if those two teams tied for the first spot. I assume that a tie for the second Wild Card would result in a one-game playoff to determine who would get to play the first Wild Card team. In that case, home field might be determined by a coin toss? And given how close the race currently is, there's always the possibility that the Mets, Cardinals, and Giants end in a three-way tie. Unless some space opens between the three teams in the next couple of weeks, I imagine that we'll be seeing an announcement from MLB about how that would be handled.