The Blue Jays' designated hitter, who was leading off the frame against Yankees left-hander Andy Pettitte, connected on a deep drive down the left-field line that appeared to strike the foul pole before bouncing back to the field.
But Yankees left fielder Jerry Hairston Jr. saw it differently from his vantage point, spotting it make contact with a fan sitting to the left of the pole.
"I saw the ball hit the fan, and he was on the other side," Hairston said. "It was obvious to me, because I was right there. I had the best look at it."
Ruiz circled the bases for what he thought was his sixth home run of the season, but led by crew chief Tim Tschida, the umpires took a second look, leaving the field through the Yankees' dugout. Pettitte thought the original call would stand up until Derek Jeter told him differently.
"I thought it was a homer," Pettitte said. "But immediately Jeet and the guys came over and said it shot off. I didn't even pay attention to how hard it was hit, but they said, 'Dude, it shot off like it hit the concrete up there.' Then I realized, maybe it did hit the concrete."
Upon closer inspection, the ball appeared conclusively to strike the blue facing just to the left of the mesh of the foul pole and was ruled a foul ball.
Yankees manager Joe Girardi said that his first inclination had not been to argue the call.
"Initially, I didn't, but then someone said that if it had hit the net, you would have seen the net move," Girardi said. "I said, 'You know what? I didn't see the net move.' The umpires got it right, and that's good for us."
The Blue Jays' run was taken off the scoreboard, and the Rogers Centre crowd booed as Tschida ordered Ruiz back to home plate to complete the at-bat. They booed again when Ruiz grounded out to third baseman Alex Rodriguez for the first out of the inning.
Ruiz got a measure of revenge when he went deep off Pettitte in the fourth inning, launching a solo shot into left-center field, nowhere near the foul pole.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.