Then he turned back to the bucket of baseballs beside him, reared back and let another one fly in the direction of one of the Majors' most harrowing hitters, hoping for the same result.
McKay is not the only pitcher used and abused by Pujols. He's just the only one who gets such treatment routinely, repetitively and, above all else, happily.
For the Cardinals, McKay, a former infielder and longtime first-base coach, serves in an important and underrated role. He is entrusted with throwing to Pujols every single day of Spring Training and the season. Each pitch -- and there are hundreds of them to Pujols and other Cardinals hitters during the course of a 15-minute batting-practice session -- is expected to hit its intended location, with the resulting rocket shots zipping to each side of the protective netting situated in front of him.
2010 Spring Training - null
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"It's something you might say is small," McKay said of this daily ritual, which he has performed for the A's and now the Cardinals over the past 27 years. "But for a player on that particular day, it might be the most important thing you do for him."
Last month, Justine Siegal made headlines when she became the first woman to throw BP to a big league club, by taking part in a morning session with the Cleveland Indians. She has since taken her talents to other spring camps in Arizona and Florida, breaking ground in the game.
As Siegal can no doubt attest, throwing BP might seem simple to the average fan, but those who do it for a living consider it an art.
And a taxing one, at that.
"It's not a job you take lightly," said Astros bullpen coach Jamie Quirk, a former big league catcher. "The good ones take pride in it."
For Quirk, pride means not only boasting about his BP prowess ("Some might be tied with me, but nobody's better," he said with a smile) but taking care of his arm and shoulder so that he'll be there when the hitters need him.
"It's draining, throwing every day," Quirk said. "But I really don't ever ask for a day off. I've had my share of cortisone shots. When I have one, you usually need a day, because it's medically required."
Yankees hitting coach Kevin Long, a southpaw who throws to his hitters on days they'll be facing a left-handed starter, estimated that an average BP session includes about 300 pitches.
These guys aren't pampered with pitch counts, obviously.
"Some days you just kind of fight through it," Long said.
The fight is endured by a wide variety of personnel. Base coaches, pitching and hitting coaches, bullpen catchers, managers, special instructors and even some media relations people have been known to toss BP for their teams.
But not every coach is capable of crafting a quality BP session. In fact, those who can are more likely to get jobs when they arise, because the club's daily needs are so rooted in the routine.
"It can definitely become important to the point where some organizations are having Minor League guys throw before they hire them," Rays hitting coach Derek Shelton said. "Being able to throw BP is an important aspect."
Hitters look for two primary attributes in a BP pitcher: consistency, first and foremost, and durability. Both of those traits lead to accountability, and the special relationship that can develop between a hitter and his BP partner.
"I've been on teams where they rotate BP pitchers," Yankees slugger Mark Teixeira said. "Every day you see somebody different. That had its pluses and minuses. But most of the time, you're going to have a guy that throws to you that you can count on."
McKay is that guy for Pujols. He served in the same capacity for Mark McGwire for many years.
"If you didn't throw, he didn't hit," McKay said. "If you had a tender back that day, you don't go out early and hit any golf balls, because you want to be there for him."
More often than not, the hitters appreciate such dedication to the cause.
"I was up in Toronto the last three years," said third-base coach Nick Leyva, who recently latched on with Clint Hurdle's staff in Pittsburgh. "I always threw to group three. Adam Lind, Lyle Overbay, Vernon Wells and Aaron Hill were in my group. I'd finish the 15 minutes every day, and there wasn't one time they didn't thank me. They call me 'Cuz.' They'd say, 'Thanks, Cuz.' It makes you feel good."
Alas, the relationship isn't always so rosy. Some players can be particularly demanding of their BP pitcher, expecting each and every pitch to hit the precise spot they dictate and voicing frustration if that spot is missed.
Wade Boggs was guilty of that attitude, back in the day. He used to expect every pitch to be down near the dirt off the back of the plate.
But a funny thing happened when Boggs became the hitting coach for the Rays in 2001 and tried to throw BP.
"It was a humbling experience for him," recalled Scott Cursi, the Rays' bullpen catcher. "All those years that he wanted a perfect BP, with the pitch far back so he could see the ball longer, when he had to throw it himself he couldn't do it."
Cursi can laugh at the memory, because Boggs grew appreciative of those who can provide the service and the two became good friends. And while some BP pitchers try to tailor their pitches to the specific requests of picky hitters like Boggs, most just try to keep the pitches down the middle, letting the ball move naturally, left to right and up and down, and letting the hitter adjust.
"My attitude is they're all cattle," Cursi said. "Some are different sizes or whatever, but you just do your best. Some days you're going to be good, some days bad. That's the human element of everything."
And of course, like anything else, among those who do this for a living, some are better than others at tossing BP.
A common belief is that former position players -- particularly catchers, who are used to throwing from up top -- tend to be better at the job than former pitchers, who are more skilled at cutting the ball (a no-no in BP) and more accustomed to a totally different throwing motion and release point.
"They're used to getting people out," McKay said. "They're paid to keep you from hitting. But in BP, the better you are, the further they hit the ball."
If you're particularly skilled at serving up the long ball, you might get to experience the greatest BP perk -- having a hitter ask you to be his partner in the annual Home Run Derby at the All-Star Game.
"That's an honor," said Quirk, who threw to Alex Rodriguez at the 2001 Derby and Lance Berkman in 2008. "That means you're doing a good job, and guys want to hit off you."
Ultimately, it is that relationship with the hitter that matters most to BP pitchers. The aching arm and endless repetition are all worth it if the hitter finds his comfort zone.
"What are we here for? We're here to make them better," Leyva said. "And if batting practice makes them better, then we've succeeded in that part of our pregame."