NEW YORK—The judge waves you into his chambers in the state Supreme Court building in Brooklyn, past the caveat taped to his wall—“;Be sure brain in gear before engaging mouth”;—and into his inner office, where foreclosure motions are piled high enough to form a minor Alpine chain.

Every week, the nation's mightiest banks come to his court seeking to take the homes of New Yorkers who cannot pay their mortgages. And nearly as often, the judge says, they file foreclosure papers speckled with errors.

He plucks out one motion and leafs through: a Deutsche Bank representative signed an affidavit claiming to be the vice president of two different banks. His office was in Kansas City, Mo., but the signature was notarized in Texas. And the bank did not even own the mortgage when it began to foreclose on the homeowner.

The judge's lips pucker as if he had inhaled a pickle; he rejected this one.

“;I'm a little guy in Brooklyn who doesn't belong to their country clubs, what can I tell you?”; he says, adding a shrug for punctuation. “;I won't accept their comedy of errors.”;

Justice Arthur M. Schack, 64, fashions himself a judicial Don Quixote, tilting at the phalanxes of bankers, foreclosure facilitators and lawyers who file motions by the bale. While national debate focuses on bank bailouts and federal aid for homeowners that has been slow in coming, the hard reckonings of the foreclosure crisis are being made in courts like his, and Schack's sympathies are clear.

He has tossed out 46 of the 102 foreclosure motions that have come before him in the last two years. And his often scathing decisions, peppered with allusions to the Croesus-like wealth of bank presidents, have attracted the respectful attention of judges and lawyers from Florida to Ohio to California. At recent judicial conferences in Chicago and Arizona, several panelists praised his rulings as a possible national model.

His opinions, too, have been greeted by a cry of affront from a bank official or two, who say this judge stands in the way of what is rightfully theirs. HSBC bank appealed a recent ruling, saying he had set a “;dangerous precedent”; by acting as “;both judge and jury,”; throwing out cases even when homeowners had not responded to foreclosure motions.

Schack, like a handful of state and federal judges, has taken a magnifying glass to the mortgage industry. In the gilded haste of the past decade, bankers handed out millions of mortgages—with terms good, bad and exotically ugly—then repackaged those loans for sale to investors from Connecticut to Singapore. Sloppiness reigned. So many papers have been lost, signatures misplaced and documents dated inaccurately that it is often not clear which bank owns the mortgage.

Schack's take is straightforward, and sends a tremor through some bank suites: If a bank cannot prove ownership, it cannot foreclose.

“;If you are going to take away someone's house, everything should be legal and correct,”; he said. “;I'm a strange guy—I don't want to put a family on the street unless it's legitimate.”;

Schack has small jowls and big black glasses, a thin mustache and not so many hairs combed across his scalp. He has the impish eyes of the high school social studies teacher he once was, aware that something untoward is probably going on at the back of his classroom.

He is Brooklyn-born and -bred, with a master's degree in history and an office loaded with autographed baseballs and photographs of the Brooklyn Dodgers. His written decisions are a free-associative trip through popular, legal and literary culture, with a sideways glance at the business pages.

Confronted with a case in which Deutsche Bank and Goldman Sachs passed a defaulted mortgage back and forth and lost track of the documents, the judge made reference to the film classic “;It's a Wonderful Life”; and the evil banker played by Lionel Barrymore.

“;Lenders should not lose sight,”; Schack wrote in that 2007 case, “;that they are dealing with humanity, not with Mr. Potter's 'rabble' and 'cattle.' Multibillion-dollar corporations must follow the same rules in the foreclosure actions as the local banks, savings and loan associations or credit unions, or else they have become the Mr. Potters of the 21st century.”;

Last year, he chastised Wells Fargo for filing error-filled papers. “;The court,”; the judge wrote, “;reminds Wells Fargo of Cassius's advice to Brutus in Act 1, Scene 2 of William Shakespeare's 'Julius Caesar': 'The fault, dear Brutus, is not in our stars, but in ourselves.' “;

Then there is a Deutsche Bank case from 2008, the juicy part of which he reads aloud:

“;The court wonders if the instant foreclosure action is a corporate 'Kansas City Shuffle,' a complex confidence game,”; he reads. “;In the 2006 film 'Lucky Number Slevin,' Mr. Goodkat, a hit man played by Bruce Willis, explains: 'A Kansas City Shuffle is when everybody looks right, you go left.' “;

The banks' reaction? Schack shrugs. “;They probably curse at me,”; he says, “;but no one is interested in some little judge.”;

Little drama attends the release of his decisions. Beaten-down homeowners rarely show up to contest foreclosure actions, and the judge scrutinizes the banks' papers in his chambers. But at legal conferences, judges and lawyers have wondered aloud why more jurists do not hold banks to tougher standards.

“;To the extent that judges examine these papers, they find exactly the same errors that Judge Schack does,”; said Katherine M. Porter, a visiting professor at the University of California, Berkeley's School of Law and a national expert in consumer credit law. “;His rulings are hardly revolutionary; it's unusual only because we so rarely hold large corporations to the rules.”;

Banks and the cottage industry of mortgage service companies and foreclosure lawyers also pay rather close attention.

A spokeswoman for OneWest Bank acknowledged that an official, confronted with a ream of foreclosure papers, had mistakenly signed for two different banks—just as the Deutsche Bank official did. Deutsche Bank, which declined to let a counsel speak on the record about any of its cases before Schack, e-mailed a PDF of a three-page pamphlet in which it claimed little responsibility for foreclosures, even though the bank's name is affixed to tens of thousands of such motions. The bank described itself as simply a trustee for investors.

Schack came to his recent prominence by a circuitous path, having worked for 14 years as public school teacher in Brooklyn. He was a union representative and once walked a picket line with his wife, Dilia, who was a teacher, too. All was well until the fiscal crisis of the 1970s.

“;Why'd I go to law school?”; he said. “;Thank Mayor Abe Beame, who froze teacher salaries.”;

He was a counsel for the Major League Baseball Players Association in the 1980s and '90s, when it was on a long winning streak against team owners. “;It was the millionaires versus the billionaires,”; he says. “;After a while, I'm sitting there thinking, 'He's making $4 million, he's making $5 million, and I'm worth about $1.98.' “;

So he threw his hat into a judicial race. He was elected to the Civil Court in 1998 and in 2003 to the Supreme Court for Brooklyn and Staten Island. His wife is a Democratic district leader; their daughter, Elaine, is a lawyer and their son, Douglas, a police officer.

Schack's duels with the banks started in 2007 as foreclosures spiked sharply. He saw a plague falling on Brooklyn, particularly its working-class black precincts. “;Banks had given out loans structured to fail,”; he said.

The judge burrowed into property record databases. He found banks without clear title, and a giant foreclosure law firm, Steven J. Baum, representing two sides in a dispute. He noted that Wells Fargo's chief executive, John G. Stumpf, made more than $11 million in 2007 while the company's total returns fell 12 percent.

“;Maybe,”; he advised the bank, “;counsel should wonder, like the court, if Mr. Stumpf was unjustly enriched at the expense of WF's stockholders.”;

He was, how to say it, mildly appalled.

“;I'm a guy from the streets of Brooklyn who happens to become a judge,”; he said. “;I see a bank giving a $500,000 mortgage on a building worth $300,000 and the interest rate is 20 percent and I ask questions, what can I tell you?”;