Is there any pitcher in baseball more liable to inspire someone to punch a wall than Oliver Perez?

Generally, you can tell how good a pitcher is by how well he repeats his delivery. The next time you’re at the ballpark watching a really good pitcher, pay attention to nothing but the spot where his trailing foot lands for an inning. You’ll probably see that it lands in the same place, over and over again, and wears a groove in the pitching mound. Watch Perez, and you’ll sometimes see this, and you’ll sometimes see the foot landing halfway off the mound, pointing toward parts unknown. It’s maddening, and leads to maddening results. The man is perfectly capable of striking out 10 through five innings, as he did yesterday, and then melting down.

With two outs in the sixth, Perez gave up two singles and a walk to load the bases, and then surrendered a hard liner to give up two runs and end his day. David Wright probably could have snared the liner, and Perez’s small collapse came after a long half inning in which he’d run the bases as the Mets sent eight batters to the plate, but a pitcher so incapable of a basic regularity in his delivery gets little benefit of the doubt. His inconsistency from season to season, game to game, and inning to inning is all of connected with his inconsistency from pitch to pitch.

Mets fans should be happy about this for two reasons, though. The first is that a less disciplined player can become a more disciplined one; the second is that a pitcher of Perez’s immense gifts would never have been traded if not for this flaw. Perez either will or won’t learn to focus, but if he does — and the first five innings of yesterday’s game, along with most of what has so far been a very good season, prove that he can — he’ll be an ace. If he doesn’t, he’ll be fitfully brilliant and very much worth having around.

That the Mets got him for, with all respect to Xavier Nady, essentially nothing is amazing — enough so that it’s already worth wondering where he might fit in the Mets’ long, glorious history of heists.

The best trade in Mets history was, in my opinion, the deal that brought Keith Hernandez to Queens from St. Louis. Hernandez was great for three years, excellent for two more, and served as the leader of the best team in franchise history; meanwhile, Neil Allen and Rick Ownbey, who went west in the exchange, were basically never heard from again. That marks the difference between the Hernandez trade and the deal that brought Mike Piazza to New York — while Preston Wilson, the key player in the Piazza deal, never became a great player, he was a very good one for Florida for several years. All told, you’d rather have something for nothing than something for something, and considering that Hernandez was at least arguably a more valuable Met than Piazza, the deal that laid the foundation for the 1986 World Championship looks like the team’s best.

Perez isn’t going to rate up there with Hernandez and Piazza unless he seriously contends for the Cy Young Award for several years and provides several more years of solid pitching after that. He does, though, have a real shot at ranking up there with two other fondly remembered Mets pitchers who were picked up for nothing: Sid Fernandez and David Cone.

Which of these two was the greater Met is largely a matter of opinion. Fernandez, who made at least 25 starts as a Met in seven different seasons, was average at worst and All-Star-caliber at his best. Cone was significantly more entertaining, if for morally dubious reasons, and was utterly brilliant at his best and almost always superb, but he didn’t pitch for the team as long. Quantity versus quality is an eternal baseball debate, one we can’t settle here. The point to note, though, is that Perez is quite capable of following either career path. Alternating near nohitters with outings in which he’s bombed off the mound in an inning, Perez could well end up an essentially average to above-average pitcher like Fernandez, the maddening idiosyncracies that kept him from his full potential turned into charming quirks by time (Inability to focus, meet inability to eat one portion). He also could turn into a mercurial genius before getting bounced out of town due to various shady antics in the bullpens and hotels of America.

Even if Perez’s Mets career resembles nothing more than a somewhat diminished version of either Cone’s or Fernandez’s, Mets fans will doubtless be pleased, and the trade, along with the ones that brought such notable personages as John Olerud and Jerry Grote to Flushing for so many rosin bags, will continue to salve the festering wounds left by the trades of Nolan Ryan and Scott Kazmir. Still, when on a day like yesterday you see what Perez is capable of when everything clicks just right for him, you can’t help but think he just might end up leaving Hernandez, Piazza, Al Leiter, Howard Johnson, and everyone else as footnotes in the annals of brazen Mets theft. If he does, he might even help lead the Mets to the two things that have always eluded them — consecutive pennants and a no-hitter. A bit of undisciplined pitching is worth suffering through for that kind of potential reward.

tmarchman@nysun.com