At least two suspected thieves on mopeds suffered broken bones when they were rammed by police cars, the Metropolitan Police commissioner has said.
Cressida Dick was unable to give a precise number or the exact nature of their injuries when asked.
The Met's new approach to deter moped gangs was announced this month.
The force shared dramatic footage of officers ramming thieves off their scooters in London.
The controversial tactic has been praised by some Londoners and former officers, while others have criticised it as dangerous.
Commissioner Cressida Dick said: "We've had to put the fear back into the criminal."
She said pursuit drivers are "supremely well trained" and the ramming method has resulted in only a "very small" number of injuries.
"At least one person who broke their arm and another who had some sort of break," she told Channel 5 on Friday.
"My officers make life-and-death decisions every day of the week, they're very accountable. They make the best possible decisions. We are in a risk business."
The Home Secretary has defended "tactical contact"
The Met chief said those who would be rammed would "have been repeatedly left in no doubt whatsoever that there's a police car right behind them.
"If you look over your shoulder and drive on as fast as possible, putting the public in danger, you should expect we will come after you."
Ms Dick also offered clarification on the reports of armed officers patrolling streets on foot in gang violence areas, saying there had been a "huge misunderstanding" around the proposal.
"I have no intention of causing armed officers to be routinely walking around the suburbs, except when it might be really necessary," she said.
"Rest assured I'm not going to ask firearm officers to do more unless there's a reason to do it. Huge misunderstanding."
More than 100,000 people have signed the petition - have you?
Tottenham MP David Lammy was among those critical of the proposal, saying it would be "an attempt to put out fire with fire" and risks turning streets "into armed battlegrounds".
Ms Dick also said she was concerned for police safety after footage emerged of Durham officers being pelted with fireworks.
"(It) absolutely looks like it's getting worse. Things are so visual now," she said.
"No officer comes to work to be assaulted. It's a crime. We should reduce the possibility of it."