"Not too easy, is it?"

From the visitors bullpen at Rogers Centre in Toronto, an American League pitcher screamed at Blue Jays right fielder Jose Bautista as he took his position late in a game in the spring of 2010.

"It's not too [f------] easy to hit home runs when you don't know what's coming!"

The enraged player and his teammates could hardly believe what they had seen in the previous inning. As they sat on the perch above the right-field bullpen at Rogers, they caught sight of a man dressed in white about 25 yards to their right, out among the blue center-field seats. And while the players watched, the man in white seemingly signaled the pitches the visiting pitcher was throwing against the Jays, according to four sources in the bullpen that day.

Toronto's home run rate on contact was 5.4 percent at home in 2010, meaning Rogers Centre boosted the Jays' rate by 1.8 percentage points, or about 50 percent. Their opponents' rate was 0.2 percentage points less than at a neutral park. Baseball Prospectus/ESPN

The players weren't exactly sure how the man in white knew what was coming -- maybe, they thought, he was receiving messages via his Bluetooth from an ally elsewhere in the stadium who had binoculars or access to the stadium feed. But they quickly picked up the wavelength of his transmissions: He was raising his arms over his head for curveballs, sliders and changeups. In other words, anything besides fastballs.

A few of the players in the bullpen turned their backs to the field to fixate on the man in white, while others watched the stadium's radar gun. As soon as each pitch was thrown, those watching the man would call out what they thought he was signaling, and those focused on the radar gun would confirm his signal. Sure enough, the man in white was raising his arms above his head before every off-speed pitch and doing nothing when the pitch being called was a fastball.

Some guys on that team had actually seen the same man making the same motions in 2009. But that had been in the last series of the season against Toronto, and they let it go. Now, stunned not only that the man in white was back but that he was accurately calling every pitch, a call was made to the dugout, and the coaching staff was given the following message: Start using multiple signs, even with no one on base.

When Bautista next came up to bat, he struck out. After the inning, he ran to right field, adjacent to the visitors 'pen, and the livid player issued Bautista a warning.

"We know what you're doing," he said, referring to the man in white, according to the player and two witnesses. "If you do it again, I'm going to hit you in the [f------] head."