Over the course of 16 seasons in the majors, the worst moment in Mark Grace’s career came in 1998 as he watched 35,000 pictures of his face fall from the sky.

"It was Mark Grace poster day at Wrigley field," Grace told ESPN.com. "Every single person got a 6-foot-2 growth chart of Mark Grace with a milk mustache holding a carton of milk."

The Chicago Cubs were playing the San Francisco Giants. In the bottom of the ninth, with the tying run on third base, all Grace had to do was hit a sacrifice fly.

"Everybody's waving their posters," said Grace, recently named assistant hitting coach for the Arizona Diamondbacks. "Everybody's yelling 'Mark Grace' and I hit a double play to end the ballgame. Thirty-five thousand posters came flying out onto the field. So yes, it was possibly the most down moment I had in my career."

In contrast, as Grace talked about the most memorable hit of his career, he remembers being nervous as he waited to face Mariano Rivera in the bottom of the ninth of Game 7 of the 2001 World Series.

"The world's full of guys that will tell you, 'I'm a refuse-to-lose guy,' or 'You got to be tougher mentally than the pitcher,'" Grace said. "That's all bulls---. What it is more than anything is the lack of fear. I'd be a liar if I [said] in those situations I wasn't nervous. Of course I was nervous; we're all human beings."

By 2001 Grace had learned to love the spotlight.

As he put it, "Baseball and confidence can be taught, I think it can. I think you can take a kid that shies away from the big moment and I think you can help him accept that moment more."

So, when he was at the plate facing Rivera to lead off the inning with the Diamondbacks trailing the Yankees 2-1, Grace had learned how to channel his nervousness into excitement.

"I just remember my attitude going into the box was 'By hook or by crook, I’ve got to get on base,'" Grace said. "Whether it's a base hit, or whether it's a walk, or if I have to stick my head in front of one and get hit -- you know, you get over a concussion in time -- that was my attitude: My job is to get on base."

Grace singled to center field, his only career hit off Rivera. His hit began the historic ninth-inning comeback for the Diamondbacks as they scored two runs and won the World Series. "That’s the funny thing about history," he said. "History kind of remembers its own path. That hit is kind of a historic hit for me, for the Diamondbacks, and for one of the greatest World Series ever played."

Throughout baseball history, a clutch hit, like Grace’s in the 2001 World Series, turns a player into a hero, turns teams into champions and propels franchises into baseball history.

Identifying clutch hitting ability is tricky. Statistical analysts argue that clutch hits exist, but clutch hitters don't. Players, past and present, say clutch hitting is a skill. They believe some players have the ability to hit better in clutch situations than in normal situations. Or maybe clutch hitting is simply not succumbing to the pressure of a big moment.

"If you're a clutch player, you're going to win games for teams. If you're not, it's going to be hard for you," Reds third baseman Todd Frazier said this past season. "So having runners in scoring position, I think that's probably the biggest stat that players should worry about."

One way to gauge clutch hits is by using leverage index (LI), which measures the intensity of a batting event: The higher the probability for one plate appearance to change the outcome of the game, the higher the leverage index. In 2014 Frazier had the most home runs in the majors (12) in high-leverage situations.

According to many major leaguers, part of the clutch-hitting skill is the ability to handle pressure.

"There's two ways to channel nervousness," said Grace, who batted .303 in his career while hitting .323 in high-leverage situations, which often come against a team's best late-inning relievers. "You can channel into fear, or you can channel it into excitement."

Jay Bruce described a similar approach: "I think that people who are able to slow the game down the most probably are more apt to be more successful in that situation; in higher-pressure situations a lot of times your heart starts racing a little bit, your adrenaline gets going a little more."

Matt Holliday, who batted .372 in high-leverage situations this year while batting .272 overall, said clutch hitting is not luck.

"There's an intensity level when you're in a big spot that kicks in," Holliday said. “An adrenaline that kicks in. It shouldn't be much different than every other at-bat, but you just can't help that naturally you are much more intense in a big situation."

Holliday said players are not immune to the atmosphere at the ballpark.

"There's definitely different adrenaline when the crowd's into it in a big spot," said Holliday. "You channel it into concentration. I've got to mentally bear down in my approach and make sure I get the pitch that I want."

What does "looking for my pitch" mean?

"It means you see [the ball] early out of the pitcher's hand," Ben Zobrist explained. "You know what the pitch is quickly. It's not like fastballs are getting on you before you are ready to swing."

Good swing mechanics play a part as well.

"It's just a matter of those mechanics being all put together at the right time when the ball is released," Zobrist said. "If those aren't right, a lot of times you have extra thoughts going on in your brain and you are thinking, 'Well, my hands need to get here and there or whatever,' and then you are not just focusing on the ball."

The right focus can also mean good plate discipline. Let's look at the plate discipline of players who had the best batting averages in high-leverage situations in 2014 (minimum 100 plate appearances):

In broad terms, these are good contact hitters. All of these top-10 guys were above the major league average in the percentage of pitches they made contact with inside the strike zone when swinging.

Zobrist talked about plate discipline. "It kind of ebbs and flows at times," he said. "When you are feeling well at the plate and you are seeing the ball, you are going to swing at the better pitches. When you are not, instead of backing off, you tend to swing at more stuff."

Jonathan Lucroy, who has been told by a psychologist that he has the ability to hyper-focus, said guys get into trouble when they try to do too much in clutch situations. "It's all mental," said the Brewers catcher. "This game is really more mental than anything. It’s amazing how mental this game can get."

As Grace discovered more than a decade ago, the ability to hit in a clutch situation comes down to confidence.

"In baseball, you’ve got a lot of people in the game that will tell you, 'You can't do this or you can't do that,'" Grace said. "I was a 24th-round draft pick. I wasn't supposed to do anything. I came up through the system with so many people telling me the things I couldn't do well enough to be a major league player."

But Grace knew that getting in the batter's box and facing the pitcher in clutch situations was fun for him. "If you don't believe in yourself, who's going to believe in you?" Grace said. "That wasn’t pressure, that was fun. I enjoyed it."