The Manatee County Sheriff's Office said a man entered the bank waving the knife above his head and demanded money, The Bradenton (Fla.) Herald reported Tuesday.
"He was yelling, 'Put it out, put it out," said customer Lenbert Bailey, 40. "The teller started putting cash on the counter."
Bailey said he considered challenging the robber but a bank employee told him to sit down.
"Absolutely, I thought about going for him, taking him down," Bailey said.
After scooping up the money, the robber left the bank. A security services employee called 911.
Deputies apprehended a suspect, identified as Brenan Cole Fountain, 31, 11 blocks from the bank, a sheriff's supervisor said.