When he's struggling, you can see it in his face, feel it in his presence. He tries not to take his struggles at the plate with him when he straps on the catcher's gear, but the depth of his desire to hit with force can make him his own worst enemy. He can be a world-class brooder.
When it is all clicking, as it was when he was enjoying a stretch of time as the Angels' designated hitter, Napoli can be awesome, one of the game's most lethal threats. But when his fortunes turn -- usually abruptly, without any notice -- he can be whatever the opposite of awesome is.
That's how it was when Napoli went through a recent 3-for-37 slide. He wasn't much fun to be around.
But then, just as swiftly as the swoon appeared, the big man was back, mashing line drives. On Tuesday night in San Francisco, in the midst of a four-hit game, Napoli finally lifted a deep one. A no-doubter, it carried deep into the seats in left-center, where not many hitters go in AT&T Park.
Napoli immediately flipped his bat, a moment after impact, and began his home run trot.
Asked later how No. 9 of the season felt, he grinned.
"It's been a long time," he said. "I don't even remember my last home run."
With eight hits in his past 18 at-bats, Napoli has raised his average 20 points to .284. He has 26 RBIs to go with the nine homers in 161 at-bats. He is slugging .516 -- only Torii Hunter at .616 is better among teammates -- and owns a .363 on-base percentage.
June 4 in Toronto, to refresh his memory, had been the last time Napoli had gone deep before his bomb Saturday against Jonathan Sanchez.
Napoli used the whole field for his four hits in that game, driving balls to left, left-center and right. His favorite power alley is right-center, when he gets those powerful arms fully extended, and he thinks that was the source of his recent struggles.
"You get frustrated when you go through something like that [3-for-37 spell] -- and I was really frustrated," Napoli said. "I stepped back, cleared my mind. I take my batting practice seriously, and I used it to get out of this thing and get comfortable again.
"I know I can hit the ball to right-center for power. I might have been trying to hit it over there too much, and I was tying myself up. I was letting the ball get too deep.
"In batting practice, I'm trying to hit line drives to gaps -- both gaps. I need to use both sides of the field and the middle."
Angels hitting coach Mickey Hatcher is a constant source of encouragement and guidance for Napoli.
"Nap's been working hard on using the whole field," manager Mike Scioscia said. "Mickey's trying to get his swing back. Nap looks a lot better now. We need him to be productive."
Another counselor is present for Napoli, and all the Angels, at all times -- the omnipresent Hunter.
"Torii told me, `You're trying to force it over there' to right-center," Napoli said. "He's always there, studying the game, seeing things and making suggestions.
"He's just an amazing player, an amazing person. He's going to pick you up every day. He's always up, even if he's tired, like everyone else. He'll say, `You've got to fire yourself up, pick yourself up and get that adrenaline going.'
"He's an unbelievable presence for the clubhouse. He leads by example -- nobody works harder than that guy -- but he'll also tell you what you need to hear. When you see a guy crashing into a wall with an eight-run lead -- or down by eight runs -- it makes you want to play harder.
"As players, you should feed off each other. And Torii is always there."
As timing would have it, Hunter appeared out of nowhere, drawing Napoli away from the interview with a firm expression.
"Let's go do some running," Hunter said. "Gotta get ready to play some hardball."
Lyle Spencer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.