Eric Dickerson -- Justin Bieber Is Dangerous

NFL Hall of Famer Eric Dickerson says he's personally witnessed Justin Bieber racing his Ferrari around the streets of Calabasas ... and tells TMZ he's worried the singer could seriously hurt someone if he doesn't slow his ass down.

We spoke to Dickerson -- who's lived in Calabsas for years -- and the NFL legend tells us he doesn't blame Keyshawn Johnson for confronting the singer yesterday.

"I've seen [Justin] driving fast around Calabasas before in the Ferrari," Dickerson says ... "It's just not safe."

Dickerson says he owns two Ferraris and understands how dangerous the car can be if an irresponsible person happens to be in the driver's seat.

"I used to drive fast," Dickerson admits ... "but that was on the freeway ... and even that wasn't safe."

As for Keyshawn's decision to follow Bieber to his home, Dickerson says -- "I don't blame Keyshawn, he's got kids ... I don't blame him for trying to get [Justin's] attention."

"I would've been the same way ... when you're a father it takes on a whole new meaning. Plus, we got that football mentality."