Jason Grimsley, a relief pitcher in his first season with the Yankees, was among those who flocked to see the movie ''Mission: Impossible'' in 1996, and as he watched Tom Cruise and an accomplice crawl through an air duct to steal secret information, memories of Grimsley's own impossible mission came back to him.

Grimsley didn't steal government secrets, but he was at the center of a heist that is part of baseball lore for its audacity and ingenuity. For the first time, Grimsley acknowledged last week that it was he who crawled through the innards of Chicago's Comiskey Park into the umpires' dressing room on July 15, 1994, to replace an illegally corked bat of his Cleveland Indians teammate Albert Belle with one that was cork-free.

''That was one of the biggest adrenaline rushes I've ever experienced,'' Grimsley said.

The Indians were in a playoff race with the White Sox as they played in Chicago, and Belle, the Indians' left fielder, was obliterating American League pitching -- when the season was ended by a strike on Aug. 12, he had a .357 average and 36 home runs.

Chicago's manager, Gene Lamont, had been tipped off that Belle might have hollowed out the barrel of his bat and filled it with cork, which makes the head of the bat lighter, increasing the speed of the swing. As is the prerogative of any manager, Lamont challenged the legality of Belle's bat in the first inning, a process that automatically prompted an umpire, Dave Phillips, to take the bat and lock it in his dressing room for later examination.