Everybody hits home runs in baseball. Everybody has home run hitters. But there are just four ace pitchers:

Clayton Kershaw.

Chris Sale.

Max Scherzer.

Dallas Keuchel.

And Keuchel is hurt.

The list was longer a couple of months ago. But Justin Verlander, Scherzer's old friend in Detroit, doesn't pitch like an ace. Madison Bumgarner, the noted dirt bike rider, will have to show everybody when he is fully healthy that he still has the arm and presence to pitch like an honest-to-God ace. Even before Noah Syndergaard got hurt, he had also started to act as if he'd come down with Matt Harvey Disease. It is a malady that often affects star New York athletes, and involves being blinded by the lights of the big city. And starting to think that they are, as the playwright in "All About Eve" once said, the piano that wrote the concerto.

Corey Kluber has been hurt this season. So you cut him some slack, of course. But he's not Kershaw, or Sale, or Scherzer. Felix Hernandez? Hasn't pitched anything like an ace for a while. Zack Greinke? He's really good, and pitching for a really good team. But whatever the "it" factor is for the top guys, he doesn't have it. Masahiro Tanaka, who was supposed to be the Yankees' ace? He pitches like one about once a month. If that. I love watching Yu Darvish. He's 6-6 with a 3.11 ERA.

An ace pitcher in the big leagues is starting to feel even more rare than an unspoken thought from LaVar Ball. And I've said it before when addressing this exact same subject: You don't simply measure an ace statistically, by earned runs or strikeouts or even won-loss records. As Buck Showalter said the last time we addressed the subject, you know one when you see one.

Bill Parcells used to say that you found out what kind of quarterback you had after he threw three interceptions and the team lost and everybody, fans and media, was screaming for the guy's backup to come in a play. An ace pitcher is the guy to whom you give the ball after your team has lost two of three or three of four and then basically stands out there and says to the other team's hitters, "See if you can hit this."

Harvey, back when he was the Dark Knight, before people were talking about his late nights, showed you what an ace looked like a few years ago against the Yankees, when the Mets and Yankees were playing one of their Interleague games, this one at the new Yankee Stadium. The Yankees had won the first game of the series, on Friday night. It would be Harvey's turn on Saturday afternoon.

Before the game, Ron Darling, working the game for SNY, smiled and said that he honestly believed that Harvey actually liked the fact that his team had lost the night before.

"For him," Darling said, "it makes the stage a little bigger, even here."

Harvey threw the holy hell out of the ball that day and his team won. Made Alex Rodriguez, in particular, looked older than the ocean. Harvey was an ace, briefly, before the injuries and controversies came, and he became what he is at the present time: Maybe the most famous 33-31 pitcher in Mets history, one who is hurt again. Harvey may get healthy and may be a decent pitcher again. He will never again be the kid that Tom Verducci nicknamed the Dark Knight of Gotham in Sports Illustrated.

An ace is what Sale has been from the time he pitched his first game for the Red Sox. An ace pitches the way Sale pitched on Monday night at Fenway Park against the Twins, after the Red Sox had just lost two of three at home to the Angels. An ace goes to 10-3 and strikes out nine as his team wins the game. American League Cy Young Award winner Rick Porcello has given up five runs a game this season. Even if Porcello was only giving up three, he was never going to be Boston's ace, not once Fenway got a load of Chris Sale.

This is what Peter Abraham wrote about Sale in The Boston Globe after the Twins game:

"Sale … dropped his earned run average to 2.77. He leads the majors with 155 strikeouts, a pace that would give him a ridiculous 330 on the season. No pitcher has done that since Hall of Famer Randy Johnson struck out 334 in 2002."

Here it is, Sale says, game after game for the Red Sox. See if you can hit it. It is as exciting as watching another ball leave another ballpark like a golf ball hit by Dustin Johnson.

This is what it was like at Fenway when Pedro Martinez was in his prime. This is what it was like in 2007 when Josh Beckett still had his fastball, and he could go into Cleveland up against CC Sabathia with the Red Sox down 3-1 in the American League Championship Series and own the Indians and the occasion. The Red Sox won. Beckett was brilliant. His team never lost another baseball game that October.

"Chris Sale," Pedro tweeted back in April, "is already surpassing everything I've done."

Everybody knows that's not true, of course. There was a time, when Martinez was young and healthy and in his prime, that he pitched like a right-handed Sandy Koufax, not just in the AL East, but in the thick of the steroid era. He was that good, all that arm and spin and mystery and magic and charisma. And strikeouts. And he made you wait for the next start the way you wait for Sale's next start. And Kershaw's. And Scherzer. And Keuchel, who is 9-0 this season, when he's healthy. Kershaw is still the best out of all of them, even if Scherzer has a lower earned run average, and so too does Keuchel, and Sale has more strikeouts.

Here is what Red Sox manager John Farrell said after Sale had beaten the Twins, a team has caused as much trouble for him across his career as any team around:

"It's a treat for us to see him pitch every fifth or sixth day."

"[Sale] strikes people out," Twins manager Paul Molitor said, "he puts the ball in play, he keeps the game moving." If you love baseball, you know that the last part sometimes feels as important as the wins and the innings Sale gives his team. Kershaw, in particular, is the same way. You get star pitchers who get it and throw it and keep doing that until their night is over and you want to throw them a parade.

There are other young pitchers in baseball who are something to see. Stephen Strasburg is one in Washington. He's 8-2 this season. He's just not an ace. He's not the Nationals' ace. That job was filled the moment that the Nationals threw money at Scherzer the way he throws fastballs past just about everybody.

There aren't many quarterbacks right now in pro football who are truly great. Tom Brady, of course. Aaron Rodgers. So maybe you can make the case that aces in the NFL are just as rare as they are in baseball. But they are very rare right now in baseball and very valuable and very precious. Just look around. And know that, as always, you know one when you see one, the way you saw one at Fenway Monday night.