The only automatic brake assist I know of is the few stick-shifts that have a “hill holder” clutch that allows you to take your foot off the brake and not roll back in the time it takes to coordinate the gas and clutch pedals. That won’t stop anything other than rolling when starting out on a hill. In no way, shape, or form will that prevent anything else, especially not a deliberate effort to mow somebody down.
The EBA system that @Mariah mentioned is a different system entirely, but it also only works when the driver hits the brakes.