Standing on first base with two outs in the bottom of the sixth inning, Howard started running to second when his teammate Marlon Byrd hit a pop fly to shallow right field. It should have been an routine out to end the inning, but Arizona Diamondbacks second baseman Didi Gregious failed to make the catch. With the score tied at 2-2, Howard rounded third base and tried to give Philadelphia the lead. Diamondbacks center fielder Ender Inciarte fielded the ball and threw a laser to catcher Miguel Montero. The throw clearly beat Howard, who tried to step around Montero but was easily tagged out.
But the Phillies began to argue that Montero was illegally blocking the plate. Part of experimental rule 7.13 says, via MLB.com: "The catcher may not block the pathway of a runner attempting to score unless he has possession of the ball. If the catcher blocks the runner before he has the ball, the umpire may call the runner safe."
The umpires reviewed the play and reversed the call. Howard was ruled safe at home, staking the Phillies a 3-2 lead. Philadelphia went on to win 4-2.