As of September, 2006, fighter practice is happening every Tuesday evening from 6:30-10:00 PM, under the stadium floodlight tower outside the right-field foul line of the northern baseball diamond. The nearest entrances are on Driggs Ave & Union Street and on Bedford Ave & North 12th Street.
Take the L train to Bedford Avenue, then walk north on Bedford to North 12th Street, the southwestern corner of the park. Look for the stadium floodlight tower.
Take the BQE to the McGuinness Blvd/Humboldt Street exit. Turn left off the ramp onto McGuinness, and go several "blocks" (loosely speaking -- there are a lot of twists, turns, and odd angles). Turn left on Driggs, go a few blocks, and you'll see the park on your right. (Not the park on your left.) Continue to Union Street, which comes in from the left, and park; the entrance is opposite Union.
Take the BQE to the Meeker Ave/Morgan St exit (the first exit in Brooklyn). Continue along Meeker, parallelling the BQE, to Driggs, which meets Meeker at a 30-degree angle on the right. Take Driggs for a few blocks and you'll see the park on your right. (Not the park on your left.) Continue to Union Street, which comes in from the left, and park; the entrance is opposite Union.
Marshals, Lord Ervald the Optimistic and Sir Valgard Stonecleaver