Slumping since All-Star break, Marlins, D’backs, Giants and Reds keeping each other in playoff race

The race for final wild card in the National League is shaping up to be a tight one.

What it hasn’t been — at least lately — is particularly good baseball.

At the end of Sunday’s games, Arizona, Miami and San Francisco were tied for that last postseason spot at 70-67. Cincinnati was percentage points behind at 71-68. None of those four teams, however, has a positive run differential. And none of them has a winning record since the All-Star break.

In fact, that quartet has gone 77-109 since the break. Because none of those teams has…