question:  Why was Halloween night chosen as the time for the rumble in the schoolyard?
context: Hoodlums fear his fury—and, for that matter, so do the cops! [Transcriber's Note: This etext was produced from Worlds of If Science Fiction, September 1961. There were Miss English and Miss Philicoff, the girls in the gilded teller cages. There was Charlie Casale, getting ten dollars dimes, six dollars nickels and four dollars pennies for his father in the grocery store down the street. There was Mrs. Dolly Daniels, withdrawing money from her savings account again. The three bank robbers looked like triplets. One of the others took the pistol away from Mister Anderson, the guard, and said to him in a low voice, "Think about retirement, my friend." The third one, who carried a black satchel like a doctor's bag, walked quickly around behind the teller's counter and started filling it with money. The man who had first spoken herded the tellers, Mr. Featherhall and the customers all over against the back wall, while the second man stayed next to Mr. Anderson and the door. Two police cars came driving down the block and a half from the precinct house to the bank, and the car with the four robbers in it lurched away from the curb and drove straight down the street toward the police station. There was so much confusion that it looked as though the bank robbers were going to get away after all. Then, after the getaway car had gone more than two blocks, it suddenly started jouncing around. Except that in the trunk lid the owner had burned in 'The Scorpion' in big black letters you could see half a block away." "If I'm making just a quick stop—I never spend more than five minutes with any one customer—I always leave the keys in the car. "It was four professional criminals, I thought you knew that. Stevenson followed Hastings' pointing finger, and saw again the crudely-lettered words, "The Scorpion" burned black into the paint of the trunk lid.
output:  Because the police would have a difficult time keeping track of so many children who were out.
options:  Because on that particular night, there were no police on patrol because of the recent issues with The Scorpion.  Because everyone was already dressed in disguise and not easily recognized.  Because the police would have a difficult time keeping track of so many children who were out.  Because the schoolyard was completely abandoned and they wouldn't need a lookout.