Timing is critical, of course.
Positioning matters a lot, too.
So does being cognizant of what's going on around you and knowing the tendencies of the guy who has the puck in front of you.
But the most important quality an effective NHL shot-blocker can have is not on-ice awareness or a feel for knowing what to do and when to do it.
No, it's far more basic than any of that.
The fundamental trait shared by everyone who routinely puts himself in front of hunks of frozen, vulcanized rubber moving at nearly 100 miles per hour is the ability to put fear -- and, perhaps, common sense -- aside and risk sacrificing his well-being for the benefit of his team.
"It's guts," said Brian Dumoulin, who finished second on the Penguins last season with 129 blocks. "It's willingness."
PAYING THE PRICE
The Penguins were reminded of the damage pucks can do when Bryan Rust was struck in the left hand by a shot late in their preseason finale at Detroit Sept. 29.
A few days later, Rust went on Long-Term Injured Reserve, which means he must miss at least 10 games and 24 days.
He's hardly the first player to get hurt when hit by a shot, intentionally or otherwise, and surely will not be the last.
If Jack Johnson didn't realize that before reaching the NHL, he learned it shortly after arriving.
"My first year, I broke my foot," he said. "Sheldon Souray hit me in the ankle. I was boxing my guy out in front, and I never saw the shot. He missed the net and hit me in the foot. He broke my foot."
While Dumoulin said his injuries caused by pucks have involved "maybe just fingers ... nothing too major," not all of his teammates have been so fortunate.
Zach Aston-Reese, for example, noted that shot-blockers are told to keep the back sides of their gloves, which are padded, facing the shooter. He added that not long after turning pro, acting on that nugget of knowledge didn't save him from an injury that sidelined him for an extended period.
"(A shot) can still hurt you on the padding," he said. "That happened to me my first year in Wilkes-Barre. It hit me on the padding, but that didn't stop the bone from breaking."
Feet are the body parts most vulnerable to being injured while blocking shots, so some players wear plastic shields that cover the front of their skates and are designed to diffuse the impact of a puck arriving at high speed. They like the protection those caps provide; others reject them because they feel their skating is impeded.
"That's the last thing I need, something slowing my feet down," Aston-Reese said.
While the fortitude required to block shots is timeless, the tactics for executing a shot-block have evolved. Players used to routinely leave their feet with the intent of smothering the puck in their midsection, but that's virtually unheard of in today's game.
Being just a little off in timing the slide could lead to some unscheduled dental work or facial reconstruction -- "If you don't slide the right way, you're in a lot of danger," Johnson said -- and odds are that the defending player will simply take himself out of the play.
"Forwards can pump-fake and go around you," Johnson said. "I feel like once you're down, you're kind of out of the play if you don't block it."
A LEARNING PROCESS
While courage is the foundation of shot-blocking, doing it well is a blend of instinct and osmosis.
The latter is necessary because learning how to block shots effectively is hockey's equivalent of training to be on a bomb-disposal unit. The benefits of actually practicing either -- whether it's putting your body in front of a fast-moving puck or trying to defuse actual explosives -- can be outweighed by the inherent perils.
Consequently, few, if any, coaches instruct players on how to block shots by actually having them get in front of pucks moving at high velocity during practices, which means players must absorb experiences and study video to develop and refine their technique.
"It's just one of those things you get a feel for," Dumoulin said. "The more you put yourself in those situations to block shots, the better you get at it. Just like anything."
There was a time when some NHL coaches would have players refine their techniques by putting themselves in front of tennis balls shot by teammates, but that doesn't happen much anymore.
Aston-Reese had a similar experience before turning pro, however.
"At school, our coach was (angry with) us because we weren't blocking shots, so he brought out those orange street hockey balls," he said. "The (defensemen) would line up at the point and we'd start on the dot in the (defensive) zone."
Although Jake Guentzel is best-known for his goal-scoring, he's not reluctant to block shots; Guentzel had 47 last season, second only to Rust among Penguins forwards.
Still, even though he's the son of a coach, Guentzel didn't have much formal instruction blocking shots during his formative years, aside from tennis-ball sessions "a couple days a year" during his college career at Nebraska-Omaha.
"You just kind of learn as you grow up," he said. "When you're younger, it's just kind of a straight leg. As you get older, you get down and take away ice and get 'bigger' out there to try to help out as much as you can."
Guentzel's 2018-19 total is particularly impressive because he rarely gets on the ice when the Penguins are shorthanded, a situation in which the importance of blocking shots spikes.
"When you're killing penalties, it's what you have to do," said Johnson, who kills a lot of penalties and, not coincidentally, blocks a lot of shots.
He led the Penguins with 147 last season, when only 21 NHL players had more.
Johnson, though, shrugged off a suggestion that he's particularly adept at that aspect of his job.
"I don't think it's that difficult of a thing," he said. "I think it's just whether you're willing to get into the shot lane."
Fair enough, although seeing a guy like Shea Weber, John Carlson or Alex Ovechkin winding up for a slap shot from 20 or so feet away might be enough to make even the most committed players rethink their choice of careers.
"You know that if (Ovechkin) hits you, it's going to suck," Johnson said. "Shea Weber is one of them. Usually, one of the forwards is up there (challenging him at the point), but if he gets it through and we're standing down there by the net ... There's a handful of guys in the league that you know that if they go to wind up, it's probably not going to be a good feeling."
SPLIT-SECOND DECISIONS
Blocking shots under optimal circumstances is challenging, but there often are complications, like deciding whether to try to get in front of the shot at all.
And self-preservation has nothing to do with it.
Getting in the path of a shot sometimes means getting in the line of sight of the guy ultimately responsible for stopping the puck, the goaltender.
His job, already difficult, gets a lot tougher if a teammate prevents him from getting a good look at a shot while making a futile attempt to block it en route to the net.
That means the defender can be obliged to analyze the situation in a few milliseconds, then decide whether going for the block is the prudent thing to do.
"It depends on where the shooter is," Johnson said. "It's very situational. Five-on-five, you're usually trying to keep a guy from getting to the net and letting the goalie do his job.
"But when you're killing penalties, you're outnumbered, so somebody's got to get in the shot lane. It's not like everyone can just box a guy out. Someone's going to be left open."
Communication with the goaltender is important, Dumoulin said, although his default position is to try to get a piece of the shot.
"You're listening to the goalie a little bit," he said. "Sometimes he says he's screened or something, so you try to use another angle. But for the most part, you're just trying to get down and just block it the best you can."
Assuming, of course, that you have the guts.
